Without Prejudice Privilege: The “unambiguous Impropriety” Exception

In Henderson & McPherson v Ministry of Defence [2026] EWHC 2645 (SCCO), the Senior Courts Costs Office provides a useful reminder of the strength of without prejudice privilege (‘WPP’). The case concerned costs schedules exchanged during negotiations and whether alleged discrepancies with later bills of costs justified lifting WPP. The Court held they did not.

The Law in Brief

WPP protects genuine settlement negotiations from being put before the court. The protection is deliberately strong, providing a “veil or cloak” of privilege, but there are several recognised exceptions to this privilege. One exception arises where “the exclusion of the evidence would act as a cloak for… unambiguous impropriety” (see Unilever v Procter & Gamble [2002] 1 WLR 2436). This prevents WPP from being used to protect genuinely improper conduct. Over the years the English courts have had to grapple on a number of occasions with what behaviour constitutes “unambiguous impropriety”. A high hurdle must