Expert Duty
Definition
The obligation, recognised across common-law jurisdictions, for a court-appointed or party-instructed expert to give an honest, independent opinion rather than an opinion tailored to help the instructing party. In England and Wales this is codified in Criminal Procedure Rule 19.
- Core obligation
- Honest, independent opinion, not one favouring the instructing party
- UK codification
- Criminal Procedure Rule 19
- Scope
- Applies whether court-appointed or party-instructed
- Jurisdictional reach
- Recognised across common-law jurisdictions
Common questions
Does the expert duty change because the expert is paid by one side?+
No. The duty to the court overrides any obligation to the paying party. Payment arrangement does not excuse a biased or selectively reasoned opinion, and courts criticize experts who let instructing-party interest shape their conclusions.
What happens if an expert breaches this duty?+
Consequences range from the court giving the opinion little or no weight, to costs sanctions against the party or expert, to referral to the expert's professional body, and in extreme cases contempt-adjacent proceedings for deliberately misleading the court.
Is the expert duty the same as being neutral between the parties?+
Not quite. The expert can still be instructed and paid by one side and hold a genuine opinion favouring that side, but the reasoning must reflect honest professional judgment rather than advocacy for the instructing party's position.
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