Clinical Negligence Expert Evidence: Breach of Duty vs Causation Reports

Last updated: 5 May 2026

Quick answer

In a clinical negligence claim you almost always need two distinct expert reports: one on breach of duty (was the treatment below an acceptable standard?) and one on causation (did that breach cause the injury?). Sometimes the breach expert can also speak to causation, but in most cases the disciplines are different — a surgeon who can opine on operative technique cannot necessarily opine on the natural progression of cancer or on neurological injury. Both reports must comply with Civil Procedure Rules Part 35 and Practice Direction 35: independent of the parties, addressed to the court, with a statement of truth and a statement of compliance with the duty to the court. Without both, the claim does not get past the Pre-Action Protocol stage.

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Why two reports

Clinical negligence has two legal hurdles that a claimant must clear:

1. Breach of duty — the treatment fell below the standard a reasonable, competent practitioner would have provided. The legal test is Bolam (treatment in line with a responsible body of medical opinion is not negligent) as refined by Bolitho (the body of opinion must itself withstand logical analysis).

2. Causation — the breach caused, or materially contributed to, the injury. The default test is "but for" causation: but for the breach, the injury would not have happened.

A clinician who can speak with authority to whether a particular operation was carried out competently is rarely the same clinician who can speak with authority to whether that operation caused a specific neurological deficit, or whether a delayed cancer diagnosis altered the survival chances by a meaningful percentage.

That is why the reports are usually divided.

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The breach-of-duty expert

The breach expert is from the same speciality as the clinician whose conduct is being criticised. A claim about a hip replacement is reviewed by an orthopaedic surgeon. A claim about a missed cancer diagnosis in primary care is reviewed by a GP. A claim about anaesthetic management is reviewed by an anaesthetist.

The expert must be:

• Currently practising or recently retired in the relevant speciality (5-10 years out is usually still acceptable)
• At a comparable seniority to the defendant clinician (consultant against consultant; senior nurse against senior nurse)
• Independent — no current or recent treating relationship with the claimant; no professional rivalry or close professional connection with the defendant
• Familiar with the standard of care at the relevant date (standards move; a 2015 case is judged by 2015 standards, not by what is taught now)

What the breach expert is asked to address:

• Was the treatment in line with a responsible body of medical opinion at the relevant time?
• If not, what should have happened?
• What were the deviations from accepted practice?
• Were any of those deviations such that no reasonable body of opinion would support them?

The report typically runs 8-25 pages. It works through the chronology, identifies the steps where breach is alleged, and applies the Bolam-Bolitho test to each.

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The causation expert

The causation expert is often from a different speciality from the breach expert. The question is biological: what did the breach actually cause?

In a delayed cancer diagnosis case:

• Breach expert (often a GP or A&E consultant): "The defendant should have referred for urgent investigation in March 2024."
• Causation expert (an oncologist): "Had the claimant been referred in March 2024, on the balance of probabilities the cancer would have been Stage 2 not Stage 4 at diagnosis. Five-year survival would have been 78% rather than 24%."

The causation expert is asking — on the balance of probabilities — what would have happened if the breach had not occurred. They use:

• The patient's actual clinical course
• Published outcome data for the relevant condition at the relevant stage
• Their own clinical experience
• Comparison with notional alternative treatment paths

What works in a causation report:

• Specific percentages or ranges, supported by published evidence
• Clear distinction between actual outcome and notional better outcome
• Acknowledgement of uncertainty (the court accepts ranges; it does not need pinpoint accuracy)

What does not work:

• Bald assertion ("The cancer would have been cured")
• Failure to engage with the published evidence
• Generic statements that could apply to any patient

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When one expert can do both

In some cases the same expert speaks to both breach and causation. Examples:

• A surgical-error case where the breach is the operation itself and the injury is the immediate surgical consequence (a damaged bile duct, a retained swab, a wrong-level spinal fusion). A surgeon can speak to whether the technique was below standard and to whether the injury followed from it.

• An anaesthetic awareness case — the anaesthetist expert can address both why the anaesthetic was inadequate and the consequence (awareness, PTSD).

• A medication-error case in a single speciality — a hospital pharmacist or a specialist physician can sometimes cover both.

But in most cases — particularly delayed-diagnosis cases, birth-injury cases, and any case involving long-term consequences — the disciplines are separate.

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Other expert disciplines often required

A serious clinical-negligence claim can need many more experts than just two. Common further roles:

A catastrophic-injury claim (severe brain injury, tetraplegia, complex obstetric injury) can run with 10-15 experts. A mid-value claim usually has 3-5.

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CPR Part 35 — what the report must contain

Practice Direction 35 paragraph 3 lists the formal requirements. A non-compliant report can be excluded from evidence.

The report must include:

• Details of the expert's qualifications
• Details of literature and material relied on
• The substance of all material instructions
• Who carried out any examinations or tests
• Where there is a range of opinion, a summary of the range
• A summary of conclusions
• A statement that the expert understands and has complied with their duty to the court
• A statement of truth in the prescribed form (PD 35 para 3.3)

The expert's primary duty under CPR rule 35.3 is to the court, overriding any obligation to the party who has instructed or paid them. This is not a formality. It is enforceable — experts have been criticised, professionally referred, and on occasion struck off for partisan reports.

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Joint statements and the meeting of experts

Once both sides have served their expert reports, the court directs that the same-discipline experts meet — without the parties or solicitors present — to discuss the issues and produce a joint statement.

The joint statement records:

• Issues on which the experts agree
• Issues on which they disagree
• Reasons for any disagreement

The narrowing effect of joint statements is one of the strongest case-management tools in clinical-negligence litigation. A claim that started with 14 disputed allegations of breach often ends a joint-statement process with 2-3 live issues for trial.

The joint statement is usually disclosed to the parties; the discussions leading to it are without prejudice.

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Finding and instructing experts

Experts are not difficult to find but they are demanding to manage.

Where to find them:

• The Royal College for the relevant speciality (specialty-specific medico-legal directories)
• The Academy of Experts and the Expert Witness Institute
• Solicitor recommendations from previous cases
• Court of Protection deputies and case managers (for support disciplines)

What to send when instructing:

• The Letter of Instruction — confidential, sets out the issues and the questions
• Medical records, in date order, paginated where possible
• Witness statements (claimant and any factual witnesses)
• Any other expert reports already obtained
• The relevant pleadings or draft pleadings

What to expect on cost:

• Breach expert in mainstream speciality: £2,000-£8,000 for the initial report
• Causation expert: £1,500-£6,000
• Care expert: £3,000-£10,000 (longer reports, more analysis)
• Catastrophic-injury cases with multiple experts: £40,000-£150,000+ in disbursements before trial

These are recoverable as disbursements if the claim succeeds. On a Conditional Fee Agreement, they are usually funded by After-The-Event insurance or by the solicitor on credit.

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How BundleCreator helps

A clinical-negligence trial bundle that includes expert evidence is one of the most demanding bundle exercises in civil litigation. The court needs:

• Each expert's report in the order specified by case-management directions
• Inter-expert correspondence and any addendum reports
• Joint statements clearly marked
• Cross-references to medical records
• A consolidated index of expert opinions on each issue

BundleCreator's Medical Negligence template orders the bundle to match the standard practice direction in clinical-negligence multi-track cases:

• Section A: Pleadings
• Section B: Witness statements
• Section C: Medical records
• Section D: Breach-of-duty experts (claimant, defendant)
• Section E: Causation experts (claimant, defendant)
• Section F: Condition and prognosis
• Section G: Care, accommodation, deputyship
• Section H: Joint statements
• Section I: Schedule of loss / counter-schedule
• Section J: Inter-party correspondence

Each expert report is bookmarked individually. The hyperlinked index lets the trial judge jump directly between (for example) the claimant's breach expert and the defendant's response on the same issue.

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Frequently asked questions

How long does an expert report take to prepare?

For a competent expert with the records to hand, eight to sixteen weeks is typical for an initial report in a moderately complex case. Catastrophic-injury cases run longer. Always agree timetables in writing at the point of instruction.

Can I see the expert before instructing them?

You should have a brief conversation (or video call) before formal instruction. Confirm availability for trial, conflict-checks, fee structure, and a rough timeline. This is normal and not a problem for the expert's independence.

What if my expert disagrees with my case?

That is exactly what experts are for. Independence means an expert is free to say the case is weak. If your expert reports adverse to your case, you have to decide whether to abandon, amend, or seek a second opinion. The CPR rules on changing experts — particularly Edwards-Tubb v JD Wetherspoon plc [2011] EWCA Civ 136 and subsequent cases (e.g. BMG (Mansfield) Ltd v Galliford Try Construction Ltd [2013] EWHC 3183 (TCC)) — are strict. The court will usually require disclosure of the original expert's report as a condition of permission to rely on a new one. Take advice before switching.

Do experts attend trial?

Often, yes. The cross-examination of opposing experts is the heart of a clinical-negligence trial. Experts sometimes give evidence concurrently ("hot tubbing") under the trial judge's direction. The trial usually takes 3-7 days for a single-issue claim; longer for multi-issue catastrophic-injury cases.

Can I use a hospital colleague as my expert?

No. Independence means no professional connection with the parties. A colleague who works in the same hospital trust as the defendant clinician cannot be the expert against them. A close professional friend cannot be the expert for them.

What is the expert's duty to the court?

CPR rule 35.3 — the expert's duty is to help the court on matters within their expertise, and that duty overrides any obligation to the party paying them. Practical effect: experts give the answer the medicine supports, not the answer that helps their client. Partisan experts get caught, criticised, and sometimes referred to their regulator.

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Further reading

• Civil Procedure Rules Part 35 — Experts and assessors
• Practice Direction 35 — Expert evidence formalities
• Pre-Action Protocol for the Resolution of Clinical Disputes
• Clinical Negligence Time Limits: The 3-Year Rule and the Date of Knowledge
• Pre-Action Protocol for Clinical Negligence: Letter of Claim Walkthrough