This guide sets out what to include, the specific questions to address, document provision, fee terms, and the differences between party-appointed and single joint expert instructions.
Essential Contents of the Letter of Instruction
Every letter of instruction should include: party details and proceedings reference; the expert's defined role (CPR Part 35 expert witness, adviser, or expert determiner); background facts agreed and in dispute; the legal framework (contract, breach alleged, measure of damages); specific questions for the expert to address; list of documents provided and where further disclosure will come from; timetable and hearing date; fee basis and budget; and confirmation that the expert's duty is to the court.
Avoid instructing the expert to 'support the claimant's case.' CPR Part 35.3 requires the expert's duty to override any obligation to the instructing party. Instructions should ask the expert to provide independent opinions on quantum, including weaknesses in the claiming party's position where identified.
For litigation privilege, mark the letter appropriately and understand that the expert's working papers may become disclosable in certain circumstances. Do not include irrelevant privileged strategy that the expert does not need to perform the analysis.
Specific Questions to Address
Specific questions focus the expert's analysis and define the scope of the report. Typical questions in contract loss cases include:
1. What was the claimant's financial position before the breach? 2. What would the financial position have been but for the breach? 3. What is the net loss of profits (or wasted expenditure) over the defined loss period? 4. For each head of consequential loss, does the loss pass the Hadley v Baxendale remoteness test on the facts provided? 5. What steps were available to mitigate loss, and what was the value of mitigation achieved or reasonably achievable? 6. What are the material assumptions, and how does the loss figure change if those assumptions are varied?
Tailor questions to the case. Construction quantum instructions should reference specific contract clauses and claim heads. Professional negligence instructions should address scope of duty and loss of chance. Avoid asking the expert to opine on legal liability or contractual interpretation unless qualified to do so.
Documents to Provide at Instruction
Provide a complete document pack at instruction to avoid delay and scope disputes. Core documents for commercial loss claims: the contract and all variations; correspondence relating to breach and mitigation; financial statements (audited, three years pre-breach); management accounts for the loss period; budgets and forecasts; invoices and payment records for wasted expenditure claims; and any prior expert reports or quantum assessments.
For construction: the contract (with amendments), programme (as-planned and as-built), extension of time notices, loss and expense applications, measured works records, and cost ledgers. For professional negligence: the retainer, advice given, the transaction documents, and evidence of the actual outcome.
Organise documents chronologically and by category with an index. Electronic data rooms are standard for larger matters. Confirm the litigation hold covers all relevant systems before the expert begins analysis.
Fee Agreement and Timetable Terms
Fee terms should be agreed in writing before work commences. Standard terms include: hourly rates by seniority; estimated hours for each phase (document review, analysis, report drafting, meetings); fixed fee for defined scope where appropriate; disbursements; payment terms; and what happens if scope expands.
Contingency fees for expert witnesses are prohibited, the expert must not have an interest in the outcome. Confirm this expressly.
Set realistic timetables with milestones: initial assessment and document request list (within 2 weeks); draft report (allow 4–8 weeks depending on complexity); final report after comments; availability for joint expert meeting and oral evidence. Urgent adjudication instructions require compressed timetables, agree premium rates and availability upfront.
CPR Part 35 Requirements and SJE Joint Instructions
CPR Part 35 and Practice Direction 35 govern expert evidence in civil proceedings. The letter should remind the expert of: the overriding duty to the court (PD 35 para 2.2); the requirement to provide opinions only on matters within their expertise; the duty to consider all material facts including those that detract from their opinion; and the format requirements for the expert report (PD 35 para 3.2).
For Single Joint Experts (SJE), both parties must agree the joint instruction. The letter should be signed by both solicitors (or approved by both after draft circulation). Agree: the questions (identical for both parties); documents to be provided (each party to supply simultaneously); fee sharing; procedure for supplemental questions; and how disagreements on instruction are resolved (typically by court application).
SJE instructions should not favour one party's case formulation. Frame questions neutrally. If the parties cannot agree on an SJE instruction, the court can determine the terms under CPR 35.7. Party-appointed experts remain the norm in high-value commercial disputes where adversarial testing of quantum is expected.
Frequently Asked Questions
When should a solicitor instruct a contract loss expert?
Instruct as early as possible once breach is alleged and quantum is in issue, typically after initial pleadings or during pre-action protocol exchange. Early instruction allows the expert to advise on document preservation, loss mitigation, and the viability of the quantum claim before trial budgets are committed.
Can solicitors amend the letter of instruction after the report is drafted?
Supplemental instructions are permitted for matters arising after the original instruction, but should not fundamentally change scope without agreeing revised fees. Material changes may require an addendum report. The opposing party is entitled to see supplemental instructions.