09 Aug WHAT IS A SINGLE JOINT EXPERT WHO SERVES AS A WITNESS IN LEGAL MATTERS?
A single joint expert, frequently abbreviated SJE, is an expert who is instructed to provide expert evidence for two or more parties in a legal proceeding on a particular issue.
In simple terms, instead of each side hiring its own expert, the parties bring in a single joint expert as a way to use one authority who is jointly instructed.
For example, imagine two parties have a dispute about whether a building has serious structural defects.
Instead of:
Party A → Expert A
and
Party B → Expert B
the court may direct:
Party A + Party B → Single Joint Expert
The expert examines the relevant evidence, applies their professional expertise, and prepares a report for the court.
The important point is that the expert is not supposed to be “Party A’s expert” or “Party B’s expert.”
The expert’s role is to assist the court on matters within their expertise.
Under CPR Part 35 in England and Wales, a single joint expert is defined as an expert instructed to prepare a report for the court on behalf of two or more parties. The rules also state that an expert’s overriding duty is to help the court on matters within the expert’s expertise, and that this duty overrides obligations to the person who instructed or paid the expert.
Why Do Courts Use Single Joint Experts?
Expert evidence can become expensive and complicated.
If two parties have completely separate experts, each expert may produce a report, charge fees, attend conferences, answer questions, and potentially testify.
That can create:
Additional costs
Longer proceedings
Conflicting expert opinions
More documents
More hearings
More opportunities for disagreement
A single joint expert can sometimes make the process more efficient.
The idea is relatively straightforward:
If the court needs specialized knowledge on one particular issue, perhaps one suitably qualified expert can address that issue for everyone.
The English and Welsh Civil Procedure Rules specifically state that expert evidence should be restricted to what is reasonably required to resolve the proceedings. The Practice Direction also says that, where possible, matters requiring expert evidence should be dealt with by only one expert.
Is a Single Joint Expert the Same as a Court-Appointed Expert?
Not necessarily.
This distinction can be confusing.
A single joint expert is jointly instructed on behalf of two or more parties.
A court-appointed expert is appointed by the court under whatever procedure applies to the proceeding.
In some cases, the court directs the parties to use a single joint expert.
Under CPR 35.7, where two or more parties want to submit expert evidence on a particular issue, the court may direct that the evidence on that issue be given by a single joint expert. If the relevant parties cannot agree on who that expert should be, the court can select an expert from a list or direct another selection procedure.
So a single joint expert may be selected by agreement between the parties, or the court may determine the selection process.
The Basic Idea
The easiest way to understand an SJE is to compare the traditional model with the joint model.
Traditional expert model
Claimant → Claimant’s expert
Defendant → Defendant’s expert
The two experts may reach different conclusions.
Single joint expert model
Claimant + Defendant → Single joint expert
The expert provides an opinion to the court on the relevant issue.
The parties can still disagree with the expert’s conclusions.
That is important.
Jointly instructing an expert does not necessarily mean that everyone agrees with the expert’s opinion.
It means the parties share the same expert rather than each presenting their own expert on that issue.
What Does a Single Joint Expert Do?
The SJE’s role depends on the issue for which they are instructed.
An SJE could be asked to examine:
Property condition
Building defects
Valuation
Medical issues
Financial matters
Accounting
Engineering
Construction
Business valuation
Vocational matters
Technology
Accident reconstruction
Other specialized subjects
The expert then applies their professional knowledge to the evidence.
For example, in a property dispute, a surveyor might be instructed to determine:
What defects exist?
What caused them?
What remedial work is necessary?
What might the remedial work cost?
The precise questions should be established in the instructions.
The Expert’s Duty Is to the Court
This is one of the most important concepts.
A single joint expert is not simply an employee of the parties.
Under CPR 35.3, an expert’s duty is to help the court on matters within their expertise. That duty overrides any obligation to the person who instructed or paid the expert.
This means the expert should not approach the assignment as:
“Which side hired me?”
Instead, the expert should approach it as:
“What does my professional expertise and the evidence show?”
That distinction is fundamental.
Does the Expert Have to Agree With Both Parties?
No.
A single joint expert does not have to produce an opinion that makes everyone happy.
Suppose a claimant believes that repairing a building will cost £100,000.
The defendant believes the cost is only £20,000.
The SJE investigates the matter and concludes that the reasonable cost is £55,000.
Neither side gets exactly what it wanted.
That does not necessarily mean the expert has failed.
The expert’s job is to provide an independent professional opinion.
Can the Parties Challenge a Single Joint Expert?
The fact that an expert is jointly instructed does not automatically mean their conclusions are unchallengeable.
The parties may have mechanisms to ask questions, challenge conclusions, present arguments about the evidence, or seek permission for further expert evidence, depending on the applicable rules and circumstances.
Under CPR 35.6, a party may put proportionate written questions to a single joint expert for clarification, generally once and within 28 days of service of the report unless the court or the other party permits otherwise. The expert’s answers are treated as part of the report.
There can also be circumstances in which a party seeks permission to rely on additional expert evidence.
The exact procedure is case-specific.
How Is a Single Joint Expert Selected?
The parties may attempt to agree on a suitable expert.
The selection process might involve exchanging names of qualified professionals.
For example:
Party A proposes three experts.
Party B reviews the candidates.
The parties agree on one.
If the parties cannot agree, the court may determine the selection process.
Under CPR 35.7, the court may select the expert from a list prepared or identified by the relevant parties or direct another method of selection.
The objective is to identify someone appropriately qualified and suitable for the particular issue.
What Qualifications Should an SJE Have?
The answer depends entirely on the subject.
A medical issue requires medical expertise.
A structural problem requires an appropriately qualified engineer or other relevant professional.
A property valuation requires someone with appropriate valuation expertise.
A financial dispute may require an accountant, economist, or valuation specialist.
The important question isn’t simply:
“Is this person an expert?”
It is:
“Is this person qualified to answer this particular question?”
Relevant factors may include:
Education
Professional qualifications
Industry experience
Practical experience
Academic research
Publications
Previous expert work
Relevant technical knowledge
Experience with similar disputes
Why Choosing the Right SJE Matters
Once a single joint expert is appointed or jointly instructed, the expert’s analysis can become extremely important to the case.
Therefore, parties should pay careful attention to the selection process.
A good SJE should ideally have:
Relevant expertise
Their knowledge should closely match the disputed issue.
Independence
They should be able to reach conclusions without favoring either side.
Communication skills
They should be able to explain complicated subjects clearly.
Methodological rigor
Their conclusions should be based on a defensible professional methodology.
Availability
They need sufficient time to complete the assignment properly.
Appropriate experience
Experience producing expert evidence can be valuable.
What Are the Instructions to a Single Joint Expert?
Instructions tell the expert what they have been asked to do.
This can be one of the most important documents in the process.
Instructions might explain:
The background
The issue requiring expert evidence
The questions the expert must answer
Documents to be reviewed
Materials to inspect
Relevant assumptions
Required examinations
Deadlines
Reporting requirements
The instructions should not improperly attempt to dictate the expert’s conclusion.
Instead, they should establish the questions the expert is being asked to answer.
Joint Instructions
Where a single joint expert is used, the parties may work together to establish instructions.
The purpose is to give the expert a common factual and procedural framework.
In England and Wales, CPR 35.8 provides that where the court directs use of a single joint expert, any relevant party may give instructions, and when a party gives instructions it must send a copy to the other relevant parties. The court can also give directions concerning fees and examinations or experiments.
This transparency is important.
One party should not secretly provide information or instructions to the SJE that the other relevant parties do not receive.
What If the Parties Cannot Agree on Instructions?
Disagreement about instructions can happen.
For example, one side may want the expert to answer five questions while the other wants ten.
Or one party may believe that certain documents are relevant while the other disagrees.
Depending on the procedural rules and court directions, the dispute may need to be resolved by the court.
The key principle is that the expert should receive an appropriate and transparent assignment rather than being privately directed by one side.
Can One Party Give Instructions to an SJE?
Yes, under the English civil procedure rules, where a court has directed use of a single joint expert, any relevant party may give instructions, but the other relevant parties must receive a copy at the same time.
This prevents one side from controlling the information given to the expert.
It also gives the other parties an opportunity to identify errors, omissions, or additional relevant material.
Who Pays the Single Joint Expert?
Expert fees can be significant.
The parties generally need to agree how the costs will be handled, subject to any applicable court directions.
Under CPR 35.8, unless the court directs otherwise, the relevant parties are jointly and severally liable for the SJE’s fees and expenses.
“Jointly and severally liable” is an important phrase.
In simple terms, it can mean that the expert may be able to seek payment of the fees from any one of the responsible parties rather than being limited to collecting only a particular party’s share.
The ultimate allocation of litigation costs can be a separate question.
A party might initially contribute to the expert’s fee and later seek recovery of costs depending on the outcome and applicable rules.
Can the Court Limit Expert Fees?
Yes, in appropriate circumstances.
CPR 35.8 provides that the court may, before an expert is instructed, limit the amount that can be paid by way of fees and expenses and may direct that some or all of the relevant parties pay money into court.
This is one reason parties should understand the proposed scope of work before an expert begins.
A narrow technical question may require substantially less work than a broad investigation involving numerous inspections, calculations, or tests.
What Does an SJE Report Look Like?
The expert will generally prepare a written report unless the court directs otherwise.
Under CPR 35.5, expert evidence is generally given in a written report unless the court directs otherwise.
A report may include:
Expert qualifications
Instructions
Materials reviewed
Facts considered
Methodology
Analysis
Findings
Opinions
Qualifications or limitations
Relevant supporting information
The precise required contents depend on the applicable rules and directions.
Why Are Limitations Important?
A good expert does not pretend to know something they cannot establish.
For example, an engineer might conclude:
“The available evidence is consistent with water ingress through the failed seal.”
But the engineer might not be able to say:
“The seal definitely failed on March 12.”
if there is insufficient evidence to establish the exact date.
Similarly, a valuation expert might provide a valuation range rather than pretending there is a mathematically precise answer when the underlying assumptions involve uncertainty.
Acknowledging limitations can increase credibility.
What Happens After the SJE Report?
Once the report has been served or disclosed according to the applicable procedure, the parties review it.
They may:
Agree with the conclusions
Disagree with some conclusions
Ask permitted questions
Seek clarification
Identify factual errors
Consider whether further expert evidence is necessary
Use the report in settlement discussions
Prepare for trial or another hearing
The report can therefore have significant strategic importance.
Can an SJE Testify in Court?
Potentially, yes.
Whether an SJE must or may attend court depends on the court’s directions and applicable procedural rules.
Expert evidence is often primarily presented in written form.
In some cases, oral evidence may be necessary.
If the expert attends court, the parties may have an opportunity to ask questions within the applicable procedural framework.
The SJE remains subject to their duty to assist the court.
Can a Party Cross-Examine a Single Joint Expert?
The answer depends on the applicable rules and court directions.
A party may have mechanisms for questioning or challenging expert evidence.
But an SJE is different from a conventional party-appointed expert because the expert is jointly instructed.
The court may regulate how and when questioning takes place.
The important point is:
Joint appointment does not make the expert immune from scrutiny.
Can a Party Hire Its Own Expert Too?
Potentially, but this depends on the applicable rules and the court’s permission or directions.
The entire purpose of an SJE is often to avoid unnecessary duplication.
If one party simply decides to obtain another expert on the same issue, that may create procedural and cost issues.
Under CPR Part 35, expert evidence requires court permission, and the court controls the extent to which expert evidence is used.
A party should therefore not assume that it can automatically appoint a second expert merely because it dislikes the SJE’s conclusion.
Can a Party Have an Adviser “Shadow” the SJE?
There can be circumstances in which a party obtains separate expert advice for internal purposes.
That is different from automatically having a second testifying expert.
For example, a solicitor might want an independent specialist to help them understand and evaluate an SJE report.
Whether that additional expert can be relied upon formally in the proceeding is a separate question governed by the applicable procedural rules.
Single Joint Expert in Property Disputes
Property disputes are a common setting for SJEs.
A surveyor might be instructed to examine:
Damp
Structural movement
Roof defects
Building condition
Defective workmanship
Repair requirements
Remedial costs
The SJE might inspect the property and prepare a report.
Both parties then have access to the same expert evidence.
In housing-related litigation, specific pre-action protocols may contain detailed provisions concerning the use of single joint experts. For example, the English housing conditions protocol includes procedures concerning proposed experts, joint instructions, and what happens if parties cannot agree.
Single Joint Expert in Financial Disputes
An SJE can also be used in disputes involving financial information.
For example:
Business valuation
Pension valuation
Share valuation
Accounting
Tax-related technical issues
Financial calculations
The expert might receive financial records from both sides and analyze them using an agreed or court-directed methodology.
The parties may disagree about the implications of the report even though they have used the same expert.
Single Joint Expert in Family Proceedings
Single joint experts also appear in family proceedings, although the rules differ from ordinary civil litigation.
For example, family cases can involve experts addressing:
Property valuation
Business valuation
Pension issues
Medical matters
Psychological questions
Other specialized issues
The Family Procedure Rules and associated Practice Directions contain specific provisions governing single joint experts.
For certain family proceedings, official guidance states that, wherever possible, expert evidence should be obtained from a single joint expert instructed by both or all parties.
The precise rules vary depending on the type of family proceeding.
Advantages of a Single Joint Expert
There are several potential advantages.
Lower Costs
One expert may cost less than two competing experts.
Less Duplication
The same professional doesn’t need to review identical evidence separately for two sides.
Greater Efficiency
The court receives one primary expert analysis on the issue.
Reduced Expert Conflict
There may be fewer situations where two experts simply disagree.
Independent Perspective
The SJE is expected to assist the court rather than act as an advocate for either side.
Simplified Evidence
The court may have fewer technical reports to consider.
These advantages help explain why procedural rules encourage the use of a single expert where appropriate.
Disadvantages of a Single Joint Expert
An SJE is not always ideal.
The Parties Lose Some Control
Neither side has its own dedicated testifying expert on that issue.
One Opinion May Not Capture Everything
The expert may interpret a complex issue differently from one or both parties.
Choosing the Wrong Expert Can Be Costly
If the expert’s specialization isn’t a good match, the resulting report may be less useful.
Parties May Disagree With the Report
Using one expert does not guarantee agreement.
Additional Evidence May Still Become Necessary
If the report raises unexpected issues, further expert evidence may sometimes be required subject to the applicable rules.
When Is a Single Joint Expert Particularly Useful?
An SJE may be especially useful when:
The issue is relatively narrow
The parties need an objective technical assessment
Duplication would be expensive
The court wants to limit expert evidence
The parties can agree on a suitably qualified professional
There is a strong need for an independent assessment
For example, if two parties simply disagree about the cost of repairing a roof, using one appropriately qualified surveyor may be more efficient than commissioning two lengthy reports.
When Might an SJE Be Less Suitable?
There may be situations where a single expert is less practical.
For example:
The technical issues are extremely complex
Multiple disciplines are involved
The parties have fundamentally different factual cases
The issue requires highly specialized expertise
The expert cannot reasonably investigate all relevant questions
The court determines that separate expert evidence is necessary
The court’s procedural directions and the particular facts are critical.
What Happens If the SJE Makes a Mistake?
An SJE is not infallible.
An expert could:
Misunderstand a fact
Overlook evidence
Make a calculation error
Use an inappropriate assumption
Misapply a methodology
Reach an unsupported conclusion
If a problem is identified, the parties may have procedural mechanisms to address it.
That could include questions, clarification, corrections, further evidence, or arguments about the weight that should be given to the report.
The appropriate response depends on the nature and significance of the alleged error.
Can the Court Ignore an SJE?
The court is the decision-maker.
An expert provides specialized evidence; the expert does not decide the legal dispute.
The judge must evaluate the evidence in the context of the entire case.
An expert’s opinion is therefore not automatically the same thing as a judicial finding.
The court may accept an opinion, reject it, accept part of it, or place different weight on different aspects of it, subject to the applicable rules and evidence.
What Is the Difference Between an SJE and an Independent Expert?
This terminology can cause confusion.
In some professional contexts, the term independent expert has a very specific meaning that is different from a single joint expert.
For example, the Royal Institution of Chartered Surveyors distinguishes between a single joint expert, who gives opinion evidence to the court, and an “independent expert” who may act under a contract or lease to determine a dispute, potentially with a decision that is final and binding.
Therefore:
Single joint expert: provides expert evidence.
Independent expert in some contractual contexts: may actually determine the dispute.
They should not automatically be treated as the same role.
What Is the Difference Between an SJE and a Party-Appointed Expert?
This is perhaps the simplest comparison.
Party-appointed expert
One party retains the expert.
Single joint expert
Two or more parties jointly instruct the expert.
A party-appointed expert may provide evidence supporting that party’s case, while still owing an overriding professional duty to the court where applicable.
An SJE is specifically instructed to provide evidence for multiple parties.
The distinction can affect:
Selection
Instructions
Communication
Fees
Evidence
Strategy
Disclosure
Challenging the opinion
How to Find a Single Joint Expert
Parties can search for suitable experts through:
Professional bodies
Expert-witness directories
Expert-witness firms
Specialist consultants
Industry associations
Universities
Professional networks
Expert-search services
The search should begin by identifying the exact subject matter.
For example:
Structural defect → structural engineer
Property valuation → valuation surveyor
Business valuation → valuation specialist
Accounting dispute → forensic accountant
Vehicle collision → accident reconstruction expert
The goal is not to find the most famous expert.
It is to find the most appropriate expert for the issue.
Questions to Ask a Potential SJE
Before agreeing to an expert, parties may want to consider:
What are your qualifications?
How much experience do you have with this specific issue?
Have you prepared expert reports before?
Have you acted as a single joint expert?
Have you testified in court?
Do you have any conflicts?
Are you available within the required timetable?
What will the work involve?
What information will you need?
What will the estimated fee be?
Are additional inspections likely?
Will testing be required?
What assumptions will need to be made?
Can you explain your methodology?
Have you previously acted for either party?
These questions can help the parties assess suitability.
The Importance of Neutrality
Perhaps the most important characteristic of an SJE is neutrality.
Imagine a property dispute.
The claimant tells the expert:
“The entire roof needs replacing.”
The defendant says:
“Only a small repair is necessary.”
The expert shouldn’t simply select whichever statement is more convenient.
Instead, the expert should inspect the evidence and answer:
“What does my professional assessment indicate?”
That may result in a conclusion that neither party expected.
That is part of the point of having a joint expert.
Why the SJE Is Not “Everyone’s Lawyer”
An SJE is not a lawyer for either side.
The expert does not:
Negotiate the case
Represent a party
Make legal arguments for a party
Decide who wins
Replace the judge
Replace the parties’ lawyers
The expert provides specialized knowledge.
The lawyers remain responsible for legal representation.
The SJE as a Bridge Between Technical Evidence and the Court
One useful way to think about an SJE is as a bridge.
On one side:
Complex professional knowledge
On the other:
The court’s decision-making process
The expert translates technical information into an understandable professional opinion.
For example:
A structural engineer can explain why cracks appeared in a building.
A forensic accountant can explain how a financial loss was calculated.
A medical expert can explain a medical condition.
A valuation specialist can explain why a property or business has a particular value.
The judge can then evaluate that evidence alongside everything else in the case.
The Future of Single Joint Experts
As disputes become increasingly technical, expert evidence is likely to remain important.
Emerging areas include:
Artificial intelligence
Cybersecurity
Digital forensics
Cryptocurrency
Data science
Autonomous vehicles
Advanced manufacturing
Environmental technology
Complex financial products
Digital surveillance
Software systems
These subjects may require expertise that lawyers and judges cannot reasonably be expected to possess themselves.
The challenge will be ensuring that experts remain appropriately qualified, independent, transparent, and capable of explaining their methodology.
Frequently Asked Questions
Does an SJE work for both sides?
In a procedural sense, the expert is jointly instructed by two or more parties. But the expert’s overriding duty is to the court where the applicable rules impose that duty.
Does an SJE have to agree with the claimant?
No.
The expert must reach their own professional conclusions.
Does an SJE have to agree with the defendant?
No.
The same principle applies.
Can both sides question the SJE?
Potentially, subject to the applicable procedural rules and court directions.
Written questions may be available for clarification, and oral questioning may be permitted in appropriate circumstances.
Who pays the SJE?
The parties normally have arrangements for sharing the expert’s fees, but the precise responsibility can depend on court directions and applicable rules. Under CPR 35.8, relevant parties are generally jointly and severally liable for an SJE’s fees unless the court directs otherwise.
Can an SJE be replaced?
Potentially, but this is not something a party should assume it can do simply because it dislikes the expert’s opinion. The applicable rules and court directions govern the process.
Can an SJE be wrong?
Yes. Experts are human and can make mistakes.
The important issue is how an alleged error is identified and addressed within the applicable procedure.
Is a single joint expert always required?
No.
Whether an SJE is used depends on the applicable rules, court directions, nature of the dispute, and circumstances of the case.
Legal Consultants and Witnesses for Law Firms
A single joint expert is an expert who is instructed to provide expert evidence on behalf of two or more parties on a particular issue in a legal proceeding.
Instead of each side hiring its own expert, the parties share one expert.
The model is designed in part to make expert evidence more focused, efficient, and proportionate.
In England and Wales, CPR Part 35 expressly allows the court to direct that expert evidence on a particular issue be given by a single joint expert. The rules also establish the expert’s overriding duty to help the court and provide mechanisms governing instructions, fees, questions, and expert evidence.
The concept can be summarized as:
One issue + multiple parties + one expert = single joint expert.
But “joint” does not mean “the parties must agree.”
A claimant and defendant can jointly instruct an expert and still disagree completely with the expert’s conclusions.
The expert’s role is to investigate the relevant issue and provide a professional opinion based on their expertise and the available evidence.
The SJE should not become an advocate for whichever party proposed them.
The expert’s value comes from independence, qualifications, methodology, and credibility.
A successful SJE process therefore depends on several things:
Choosing the right expert.
Defining the right questions.
Providing appropriate information.
Maintaining transparency between the parties.
Allowing the expert to exercise independent professional judgment.
Understanding the expert’s limitations.
Following the applicable procedural rules.
For parties, one of the biggest advantages is efficiency.
Instead of paying two experts to investigate the same question, the parties may obtain one professional assessment.
For the court, the benefit can be a more focused body of expert evidence.
For the expert, however, the role carries an important responsibility: the expert must not simply try to satisfy the parties who are paying the bill. Their professional analysis must be directed toward assisting the court.
That is why the single joint expert is fundamentally different from the idea of a “shared advocate.”
The expert does not represent everyone.
The expert provides expertise for the benefit of the court.
Ultimately, the purpose of a single joint expert is to help transform a technical dispute into information that a court can understand and evaluate.
Whether the subject is a building defect, business valuation, medical question, financial calculation, engineering problem, property dispute, or another specialized issue, the SJE provides a common professional reference point.
The parties may agree with the expert.
They may disagree with the expert.
They may challenge aspects of the analysis where the applicable rules permit them to do so.
But the fundamental purpose remains the same:
One qualified expert provides an independent professional assessment of a specialized issue so that the court can make a better-informed decision.
That is the essence of a single joint expert.
