CPR Part 35 — For Pool Slip Experts

The overriding duty

CPR 35.3 establishes that the expert's overriding duty is to the court — not to the party who instructed and pays the expert. This is the foundation of expert evidence under English law. An expert who advocates for the instructing party, conceals adverse findings or shapes opinion to fit the instructing party's case is in breach of Part 35 and produces evidence that collapses on cross-examination.

For pool slip experts, this means: the data is the data. If the test result favours one side clearly, the report says so — even where both sides hoped for a more nuanced outcome.

Mandatory report content

CPR Practice Direction 35 specifies what every expert report must contain. For a pool slip report:

• The expert's qualifications
• Details of any literature or other material relied upon
• A statement setting out the substance of all material instructions
• Identification of facts the expert was asked to assume
• Where the expert is not able to give an opinion without qualification, the qualification
• A summary of the conclusions reached
• Statement that the expert understands their duty to the court and has complied with it
• Statement of truth in the form prescribed by Practice Direction 22

Reports without these elements are exposed to admissibility challenge.

Range of opinion — pool-specific examples

Where there is a range of legitimate opinion on a pool slip matter, the report must summarise the range and give reasons for the expert's own opinion within it. Common examples in pool work:

• The PTV result is in the moderate band (25–35) and reasonable experts might differ on whether the surround presents an actionable risk in the specific operational context
• The cause of an unusual contamination at the time of the incident is uncertain; experts might differ on what most likely caused the surface to be in the condition it was
• Where photographs of the incident scene are limited, experts might differ on whether the photographs support the claimant's or defendant's account

The Part 35-compliant approach is to set out the considerations either way and explain the expert's reasoning.

Single joint experts (CPR 35.7)

For lower-value pool claims, the parties may agree to instruct a single joint expert under CPR 35.7. Both parties share the cost (usually equally), agree the letter of instruction, and receive the report simultaneously. The expert's duty is unchanged — the duty is to the court.

Written questions to experts (CPR 35.6)

Each party may put written questions to the other party's expert, intended to clarify the report's content. The expert's answers are treated as part of the report. This is a useful early step that often resolves apparent disagreements without requiring an experts' meeting.

Discussions between experts (CPR 35.12)

Where each party has appointed their own expert, the court may direct that the experts meet to identify points of agreement and disagreement and produce a joint statement. This is one of the most useful procedural mechanisms in Part 35 — narrowing the technical issues before trial and often producing settlements when the experts substantially agree.

Oral evidence at trial

Where matters proceed to trial, the expert may be required to give oral evidence and undergo cross-examination. The strength of the report is the foundation, but the strength of the expert in the witness box matters too. Methodology that withstood internal review must also withstand opposing counsel's cross-examination — which is one of the reasons UKAS-accredited methodology and clear, neutral writing pay dividends in litigation.

When the duty cuts the other way

The Part 35 duty applies regardless of which party instructs. Where we are instructed by a hotel operator defendant and the test data shows non-compliance, the report says so. Where we are instructed by a claimant and the test data does not support the claim, the report says so. Over time, this is what makes a report defensible — the expert who only tells the instructing party what they want to hear has no enduring credibility.