Expert Witness vs Litigation Support under CPR Part 35

Commercial disputes frequently require financial analysis long before any expert report is exchanged. Solicitors must understand the critical distinction between litigation support (typically privileged advisory work for the legal team) and expert witness appointments (independent opinions disclosed to all parties under CPR Part 35).

Why the distinction matters

The Court of Appeal and trial courts have repeatedly emphasised that an expert's primary duty is to the court, not the instructing party. CPR Part 35.3 states this expressly. When financial analysis is performed behind the scenes to help counsel understand the claim, assess settlement or prepare cross-examination, that work may fall within litigation privilege - provided it is not deployed in a way that compromises a subsequent expert appointment.

Conversely, once a formal expert is appointed, their report and communications in that capacity are subject to disclosure rules. Mixing roles without clear boundaries creates risk: an expert who has effectively advocated for one party's quantum theory may struggle to demonstrate independence.

Litigation support: typical scope

Litigation support for commercial disputes often includes:

• Early assessment of whether a quantum claim is credible
• Review of management accounts and forecasts before expert instructions are issued
• Preparation of questions for examination of the opposing financial witness
• Scenario modelling for without-prejudice settlement meetings
• Assistance drafting the letter of instruction to a forensic accountant

This work product is generally intended for the solicitor's eyes and should be structured to preserve privilege. It does not replace the need for an independent expert where the court requires expert evidence on financial issues.

Expert witness appointments

A commercial dispute expert witness provides opinions that go to all parties. Under Practice Direction 35, the expert report must set out qualifications, instructions, documents relied upon, assumptions, opinions and a statement of truth. The expert must not omit material facts that detract from the instructed party's case.

For solicitors, the practical question is timing: instruct litigation support early to shape strategy; appoint the expert when pleadings and disclosure make the financial issues sufficiently concrete.

Party-appointed vs Single Joint Expert

Party-appointed experts are instructed by one side. Single Joint Experts (SJEs) are appointed by the court or agreed between parties to provide one opinion on a given issue. SJEs can reduce costs but require careful joint instructions. The same professional may not always be suitable for both roles on the same case if prior advisory work would create a conflict.

Practical tips for instructions

1. Separate engagement letters for advisory and expert work.
2. Document the scope of any pre-appointment financial review.
3. Run conflict checks before formal expert appointment, especially in multi-party construction or shareholder disputes.
4. Align questions in the letter of instruction with pleaded case theory - experts quantify; they do not plead.

When to instruct a commercial dispute expert

Instruct a forensic accounting expert witness when the dispute requires independent evidence on loss of profits, business valuation, business interruption, breach of contract quantum or professional negligence damages. Instruct litigation support when you need privileged financial insight without immediate disclosure.

For further guidance on our engagement process, see how to instruct us or our commercial dispute expert witness service page.