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The Role of an Expert Witness

In order for a patient to commence a legal claim against a clinician, they must appoint an expert to advise on questions of liability, and issue a Letter of Claim outlining the allegations of negligence and allow the Defendant to investigate and respond. The instruction of an expert witness is critical in order to establish a claim/defence. No medical negligence claim can proceed in the absence of expert evidence. This article seeks to set out the role of the expert witness when clinical disputes arise.

How do you establish a claim in negligence?

In order for a claim to be established, the Claimant must prove the following:

  1. The doctor owed them a duty of care
  2. That duty of care was breached
  3. That breach caused injury
  4. The injury caused loss

In order to establish the above tests, the Claimant will rely on expert evidence. Equally, in order to defend a claim of negligence, the Defendant will appoint an expert to advise. The first part of the test is established when a doctor/patient relationship arises. This is not always clear-cut in the circumstances and the court will be required to determine if a duty of care is owed based on the test laid down in Caparo. Once a duty is established, then the expert will comment on breach and causation, effectively parts 2-4 of the above test.

Duty of the Expert Witness

The overriding duty of the expert witness is to advise the court and provide a neutral, unbiased view of the standard of care provided by the medical staff. This duty overrides any duty to the parties instructing the expert. On the issue of liability, the expert is instructed to advise in the context of the test set down in the case as follows:

“If a doctor reaches the standard of a responsible body of medical opinion, he is not negligent.”

It should be noted, that whilst the foundation of any clinical dispute is based on expert evidence advising the court, the court ultimately has to determine within its own “independent logical analysis” in accordance with Bolam whether the defendant has breached its duty of care. This clarification was made in the case of Bolitho, where it was determined that only the court can establish what a responsible body of medical opinion is, based on the evidence before it.

Responsible Body of Medical Opinion

In the case of Bolam, Mr Justice McNair stated:

“A doctor is not guilty of negligence if he has acted in accordance with a practice accepted as proper by a responsible body of medical men skilled in that particular art. … Putting it the other way round, a doctor is not negligent if he is acting in accordance with such a practice, merely because there is a body of opinion that takes a contrary view.”

Case law establishes that a responsible body of medical opinion can be a body of one, as determined in the case of Sullivan. In this case, the cardiothoracic surgeon was the only known medical person performing Hemi-Fontan surgery in minors by cooling to 24 degrees as opposed to the standard 18 degrees. In that case, the expert for the Defendant concluded that over a 20 year clinical practice, the clinician had established that his practice of cooling to only 24 degrees was reasonable. The court, after considering all the evidence, determined in favour of the defence.

As can be seen, expert evidence in respect of outlining a reasonable body of medical opinion is crucial to aid the court in reaching its determination in respect of liability.


In order for an expert witness to take a view on liability, they will require to review the following:

  1. Medical records
  2. Witness statements (Claimant and Defendant)
  3. Any other expert opinion
  4. Complete a literature review as to what is deemed a reasonable body of medical opinion at the relevant time of the incident
  5. Reliance on their own skill and experience

As noted above, the expert witnesses’ overriding duty is to the court. Therefore, it is reasonable for them to conclude that whilst they may not have proceeded in the same manner as the treating clinician did, nevertheless, other clinicians would have done so, and thus, the duty did not fall below a reasonable standard. It is important to note that your appointed expert does not necessarily have to conduct treatment in the same way as the defendant clinician would have done, they simply have to recognise that the way treatment was provided would be considered reasonable by a body of like minded doctors.

Competent Expert Witness

Any expert who accepts instructions must ensure that they have the correct skill and experience in order to provide an opinion to the court. In the case of Robinson, the court awarded wasted costs against the expert for a “flagrant disregard” for his duties to the court. In this case, the expert admitted at trial that he had never worked in a hospital or had any experience of extraction of a tooth under general anaesthetic (the basis of the claim of negligence). The case collapsed and the expert was held personally liable for wasted costs in the sum of £50,500. It is important to note that expert witnesses are no longer protected by immunity laws, and therefore if they are found to be in breach of their duties to the court, they can face criminal sanction in the form of fines and/or a custodial sentence.

Where Bolam does not apply

Following the case of Montgomery the test for determining whether a breach of duty has occurred in respect of informed consent has been modified. The correct test for experts to determine in such cases is as follows:

“an adult person of sound mind is entitled to decide which, if any, of the available forms of treatment to undergo, and her consent must be obtained before treatment interfering with her bodily integrity is undertaken. The doctor is therefore under a duty to take reasonable care to ensure that the patient is aware of any material risks involved in any recommended treatment, and of any reasonable alternative of variant treatments”

In the case of informed consent, the expert witness therefore has to advise the court on whether there is sufficient evidence, based on medical records and witness evidence, that the patient was provided with all relevant information relating to material risks from the patient’s perspective. Therefore, it is no longer what a reasonable body of medical opinion would have advised, it is whether the individual doctor took the time to identify what the patient would consider to be a material risk to them as an individual patient.

Your interaction with the Expert Witness

Your legal team will ask you to set out the care you provided to the Claimant. That evidence will be passed to the expert witness for consideration. It is also likely that in due course, you will be asked to attend a conference with Counsel and the expert in order to test the evidence. It is important to remember that whilst the expert is instructed on behalf of your defence, the expert remains independent and must advise your legal team based on his/her own opinion on review of all the evidence.


Expert witnesses have to be appointed by the legal parties in order to issue/defend a claim in medical negligence. The role of the expert is as follows:

  • To advise the court as to issues of liability on review of all the evidence (CPR 35)
  • To set out the standard of care in accordance with the test laid down in Bolam
  • To allow the court to conclude liability in accordance with Bolitho
  • To guide the court as to whether there is evidence of informed consent within the records/statements
  • To guide instructing solicitors as to the strength of their claim/defence

Information correct at time of publication June 2022

This article references the legal position in England and Wales, but does not necessarily reflect the position in other jurisdictions. Anyone outside England and Wales should contact PMP for further guidance.
This document does not constitute legal or medical advice and should not be construed as rules or establishing a standard of care. We recommend that you seek independent legal and/or professional advice in relation to your legal or medical obligations or rights. Premium Medical Protection Limited is the owner of this material and its contents are protected by copyright law © 2022. All such rights are reserved.
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