Out-Law Guide 3 min. read

Expert witnesses and expert advisers

There is an important distinction between instructing an expert to provide evidence in court proceedings and instructing an expert to act solely in an advisory capacity.

This guide looks at that distinction.

Expert witnesses

An expert witness' main function is to provide his independent expert opinion to the court, based on the information provided by those instructing him. Permission of the court must be obtained before a party can rely on such evidence. An expert's duty is to assist the court – this overrides any obligation to the instructing party, regardless of whether he is being paid for his services. The material instructions given to an expert witness must be included in the expert's report.

In large or complex cases the court will usually allow each party to instruct its own expert to provide evidence on an issue or particular issues. If expert evidence is needed in more than one area of expertise, the court will allow the appointment of more than one expert witness for each party. For example, in a construction dispute where the ceiling of a building has collapsed and there is a claim for the costs of repair, there may be the need for expert evidence from an engineer about the reason for the collapse and from a quantity surveyor as to the costs of repair.

The court also has the power – more often in less complex cases – to order that the parties appoint and instruct a single joint expert. Again, this expert's overriding duty is to the court.

If the court decided that an expert witness has not established his independence or complied with his overriding duty to the court, this may result in that expert's evidence being ignored or given little weight and could have costs implications.

The expert witnesses' fees may be payable by the losing party to the dispute.

Expert adviser

An expert adviser can be appointed by a party to assist in the formulation and preparation of a party's claim or defence. He has an overriding duty to those instructing him and not the court, but this will normally include an obligation to the client to explain both the strengths and weaknesses of both sides' cases. The instructions given to an expert adviser will invariably be privileged from disclosure and therefore not discloseable to the other party. For more information about privilege, see our separate OUT-LAW Guide.

In larger and more complex cases, parties sometimes use an expert adviser to liaise with the expert witness and use the expert adviser as a sounding board.

In some circumstances, expert advisers may change their role to an expert witness, although this needs to be considered carefully to ensure the expert can provide  independent expert opinion notwithstanding their earlier involvement. If this happens then a new set of instructions will be provided to the expert.

The fees incurred as a result of appointing an expert adviser may not be recoverable from the other party, even if the other party is ordered to pay your costs.

Instructions and privilege

It is important to remember that the expert witness must set out the instructions he has received in his expert report - these are not protected by privilege. This covers all the information the expert witness has been provided with, so it is necessary to consider what information and documents are provided to the expert.

The original instructions to an expert adviser who is subsequently appointed as a court-appointed expert will usually be privileged from disclosure to the other party. However to ensure these instructions will not be discloseable, new instructions should be provided to the expert in his role as a court-appointed expert witness.

Independence of the expert

An expert witnessappointed pursuant to the court's permission will usually be completely independent of either party. Although the court can permit employees - or other related persons - of a party to be expert witnesses if appropriate, the employee-turned-expert must still comply with his overriding duty to the court.

'Expert shopping' is frowned upon. Although a party may change its expert, it can only do so with permission of the court (depending on the timing of such change) and the original expert's report will usually still need to be provided to the court and the other party.

Although parties can identify the issues to be dealt with in experts' reports, the report must be drafted by the expert himself.

Expert witnesses do not have immunity from suit and can be sued for negligence arising out of the performance of their duties.

How to choose the right expert?

Your lawyer will be able to help you choose expert advisers and expert witnesses by reference to matters such as areas of expertise, professional and academic qualifications and level of indemnity insurance.


The cost of instructing an expert adviser may not be recoverable from the losing party. The cost of instructing a court-appointed expert may be recoverable from the losing party, although the instructing party will still have an overriding responsibility to pay the expert witnesses' fees. For more information on the rules on recovery of costs see our guide on costs recovery.

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