How Is Expert Evidence Used in Complex Litigation?

Expert evidence can play an important role in complex litigation where the court needs specialist knowledge to understand a medical, technical, financial or other issue outside ordinary legal experience.

Not every legal case requires an expert. Whether expert evidence is necessary will depend on the issues in dispute, the type of proceedings and whether specialist opinion is needed to help establish or assess part of the case.

Where experts are instructed in civil proceedings in Northern Ireland, their role is not simply to support the party who has instructed them. Their overriding duty is to assist the court on matters within their expertise.

What Is Expert Evidence?

Expert evidence is evidence provided by someone with specialist knowledge, qualifications or experience relevant to an issue in the proceedings.

Unlike an ordinary witness, who generally gives evidence about facts they personally saw, heard or experienced, an expert may be asked to provide a professional opinion.

The type of expert required will depend entirely on the issues involved in the case.

Examples may include:

• medical consultants and other healthcare professionals;
• accountants and financial experts;
• engineers;
• surveyors;
• care and rehabilitation specialists;
• employment or vocational experts; and
• other technical or specialist professionals.

When Might Expert Evidence Be Needed?

An expert may be required where an important issue cannot properly be assessed without specialist knowledge.

For example, in a medical negligence case, independent medical opinion may be required to consider the standard of care provided, whether a particular act or omission caused harm, the extent of an injury or the likely future prognosis.

In another type of complex dispute, an expert may be needed to assess financial loss, the condition of a building, engineering evidence or another technical question.

Before instructing an expert, consideration should be given to whether the evidence is genuinely necessary and proportionate to the issues in the case.

What Is the Expert's Duty?

An expert witness must provide an independent professional opinion.

Although the expert may have been instructed and paid by one of the parties, their overriding duty when giving evidence for civil proceedings is to help the court on matters within their expertise.

This means the expert should not act as an advocate for the person who instructed them or shape an opinion simply to support that party's case.

An expert should also make clear where an issue falls outside their expertise, where further information is needed or where an opinion is provisional or qualified.

How Is the Right Expert Chosen?

Selecting an appropriate expert can be an important part of managing complex litigation.

The expert should have suitable knowledge and experience for the particular issue being considered. It is not enough for someone to have general expertise if the case requires a much more specialised area of professional knowledge.

Consideration may also need to be given to whether the expert:

• has experience relevant to the particular issue;
• understands their duties as an expert witness;
• can provide a report within the required timetable;
• is available to participate in expert discussions where required;
• could attend court if necessary; and
• has any potential conflict of interest.

The Northern Ireland Judiciary's guidance also emphasises proportionality, including the cost and complexity of the case, when deciding whether expert evidence is required.

What Information Is Given to an Expert?

An expert should be given clear instructions explaining what they are being asked to consider.

Depending on the case, they may also receive documents such as pleadings, correspondence, records, reports, photographs, financial information or other relevant material.

In medical litigation, for example, this can include medical records, test results, imaging and reports from other clinicians.

The expert should have access to the relevant information needed to form a proper opinion. They should also identify the facts and materials on which their conclusions are based.

What Does an Expert Report Contain?

An expert report should explain the expert's opinion and the reasoning behind it.

The report should distinguish between facts that the expert knows personally, facts they have been asked to assume and the professional opinions they have reached.

It may also identify relevant research, professional literature, investigations or other material relied upon.

Current Northern Ireland High Court guidance requires expert reports to contain an expert declaration and to be verified by a statement of truth.

The purpose is to make the basis of the expert's evidence transparent to the parties and the court.

Can Experts on Opposing Sides Disagree?

Yes. It is common for experts instructed by different parties to reach different opinions about some aspects of a case.

The fact that experts disagree does not necessarily mean that either expert has acted improperly. Different professional conclusions can arise from the same evidence, particularly where the issues are technically difficult or involve professional judgement.

Where disagreement exists, the important question is usually why the experts have reached different conclusions and what evidence or assumptions underpin those opinions.

Do Experts Meet With Each Other?

They can.

The court may direct experts to discuss the issues in the case, or the parties may agree that discussions should take place.

The purpose is generally to identify the expert issues, establish where agreement exists and narrow the areas that remain disputed.

Expert discussions can therefore make a complex case easier to manage by identifying which technical matters genuinely require determination.

An expert remains independent during this process and should not be pressured to maintain an earlier opinion if the evidence or discussion leads them to a different professional conclusion.

Can an Expert Change Their Opinion?

Yes.

An expert's obligation is to provide an honest and independent professional opinion. If further evidence becomes available or the expert concludes that an earlier opinion should change, that change should be communicated and explained.

A genuine change of professional opinion is different from altering a report simply to strengthen the case of the party who instructed the expert.

Northern Ireland Judiciary guidance makes clear that experts should not be asked to amend their reports in a way that distorts their true opinion.

Does an Expert Have to Attend Court?

Not always.

Some expert issues may be agreed before trial, and in other cases the expert's written report may deal with the relevant question without the expert ultimately being required to give oral evidence.

Where important expert issues remain disputed, however, an expert may be required to attend court and explain their opinion.

The expert may then be questioned about their conclusions, the evidence on which those conclusions are based and any differences between their opinion and that of another expert.

Who Pays for Expert Evidence?

Expert evidence can represent a significant cost in complex litigation.

Fees can arise for reviewing documents, examinations or assessments, preparing reports, responding to questions, participating in expert meetings and attending court.

How those costs are funded will depend on the circumstances of the case and the funding arrangements available.

You can read more about funding and costs in a complex legal claim, including private funding, legal aid and legal expenses insurance.

How Does Expert Evidence Fit Into a Complex Legal Case?

Expert evidence is normally one part of the wider evidential picture rather than a case in itself.

A solicitor may need to consider expert opinion alongside witness evidence, records, correspondence, factual evidence and the relevant legal principles.

The timing of expert instructions can also matter. In some cases an early expert opinion may help determine whether there is a viable basis for progressing the claim. In others, further factual evidence may need to be obtained before an expert can provide a meaningful opinion.

Our guide to managing complex legal cases in Northern Ireland explains how evidence, expert input, case strategy and court procedure may fit together as litigation develops.

Expert Evidence in Northern Ireland Litigation

The appropriate use of expert evidence depends on the individual case.

Some proceedings may involve one expert addressing a single specialist issue, while particularly complex litigation can involve several experts from different disciplines.

The objective should not be to obtain as many expert reports as possible. Expert evidence should address matters that are genuinely relevant to the issues the court may need to determine.

P.A. Duffy & Co advises clients in complex matters involving areas including medical negligence, serious personal injury, human rights and public law, inquests and other substantial litigation.

Where expert evidence is required, the appropriate specialist, scope of instruction, timing and cost should be considered as part of the wider strategy for the case.

Dažnai užduodami klausimai

What is an expert witness?

An expert witness is a person with specialist knowledge, training or experience who may provide an independent professional opinion on an issue relevant to legal proceedings.

Does an expert witness work for my solicitor?

An expert may be instructed by your solicitor, but when providing evidence for civil proceedings the expert's overriding duty is to assist the court on matters within their expertise. Their opinion should remain independent.

Does every complex legal case need an expert?

No. Expert evidence should generally be obtained where specialist opinion is necessary to address an issue in the case. Whether an expert is required depends on the facts, legal issues and type of proceedings.

Can two expert witnesses disagree?

Yes. Experts may reasonably reach different professional opinions. They may be asked to discuss the issues in order to identify areas of agreement and clarify the matters that remain disputed.

Can an expert change their opinion during a case?

Yes. If new evidence or further consideration changes an expert's professional opinion, that change should be explained. An expert should not maintain an opinion simply because it previously supported the party who instructed them.