How to Instruct a Damages Expert Witness

Instructing the right damages expert witness at the right time reduces costs, narrows issues, and produces court-ready quantum evidence. This guide is structured for the three audiences DamagesExpertWitness.co.uk serves: personal injury and clinical negligence solicitors, commercial litigation teams, and international arbitration counsel.

Three Audiences, One Process

PI and clinical negligence: instruct forensic accountants (often APIL-accredited) for Schedules of Loss; actuaries for complex pension and PPO work. Commercial litigation: instruct forensic accountants for but-for lost profits and consequential loss. International arbitration: instruct economists with IBA Rules experience, DCF capability, and witness conferencing preparation. Steps 1–3 tailor the framework; steps 4–7 are common to all forums.

Seven-Step Instruction Timeline

1. 1

   Identify Your Practice Area

   Determine which audience and procedural framework applies: personal injury or clinical negligence (loss of earnings, care, pension); commercial litigation (lost profits, wasted expenditure, IP); family financial remedy (FPR Part 25); or international arbitration (ICC, LCIA, ICSID, UNCITRAL). Our practice areas hub routes each audience to the right experts and case types.
2. 2

   Identify Heads of Loss

   List every pecuniary head requiring quantification: earnings, pension, care, accommodation, lost profits, consequential loss, account of profits, or treaty damages. Cross-check against the types of damages guide and relevant service pages. Instruct actuarial input early if defined benefit pension loss or PPO modelling is in issue.
3. 3

   Confirm Civil, Family, or Arbitration Framework

   CPR Part 35 applies in civil courts in England and Wales. FPR Part 25 applies in family financial remedy proceedings (court permission and fee approval may be required). International arbitration follows institutional rules and the IBA Rules on the Taking of Evidence - confirm the procedural timetable for expert reports and any tribunal directions on witness conferencing.
4. 4

   Decide: Single Joint Expert or Party-Appointed Expert?

   The choice between a Single Joint Expert (SJE) and party-appointed experts (PAEs) affects cost, adversarial strategy, and timetable. Consider claim value, complexity, and whether the court is likely to direct an SJE at the CMC.

   Factor	Single Joint Expert (SJE)	Party-Appointed Expert (PAE)
   Appointment	Joint instruction or court direction under CPR 35.7	Each party instructs own expert
   Cost	Typically shared equally; one report	Two (or more) reports; joint meeting and statement
   Best for	Lower-value PI, straightforward quantum	High-value clinical negligence, commercial, arbitration
   Letter of instruction	Joint letter agreed by both parties or court-settled	Separate confidential instructions per party
   Testing evidence	Cross-examination of single expert	Competing reports; CPR 35.12 joint statement
   Arbitration	Tribunal-appointed expert under IBA Art 6	Party experts under IBA Art 5; hot-tubbing common

   Hot-tubbing and witness conferencing (arbitration)

   In international arbitration, tribunals frequently use witness conferencing - colloquially "hot-tubbing" - where experts give evidence concurrently and respond to each other's and counsel's questions. This is distinct from sequential cross-examination in English court trials. Prepare party experts for joint sessions: agree methodology differences in advance, produce IBA-compliant reports with clear assumptions, and consider a pre-hearing expert meeting to identify agreements. Our arbitration quantum guide covers tribunal-appointed experts and Chorzów Factory quantification.

5. 5

   Verify Qualifications and Independence

   Confirm ACA/FCA, FIA, or PhD credentials as appropriate, APIL accreditation for PI, CPR Part 35 compliance, professional indemnity insurance, and no conflict of interest. See our qualifications page and red flags checklist.
6. 6

   Prepare the Letter of Instruction

   The letter should identify issues for the expert, set out agreed and disputed facts, specify the legal framework without asking for legal advice, list documents provided, state the timetable, and address fees. For an SJE, agree the joint letter with the opponent or seek court determination of disputed terms. See the SJE guide.
7. 7

   Provide Documents and Manage the Timetable

   Supply complete financial records, pleadings, medical and care expert reports (where relevant), and prior expert reports. Agree extensions in writing if disclosure is late. Update the expert before trial if new evidence materially changes quantum. Submit your instruction via our contact form for a matched expert within one business day.

For fee expectations and cost recovery, agree terms in your letter of instruction before work begins. For CPR duties and credentials, see qualifications and our glossary.