A defence that, before the claimant started proceedings, the defendant unconditionally offered to the claimant the amount due.
Note that this defence is not available where the claim is for unliquidated damages (Greenwood v Sutcliffe [1892] 1 Ch. 1, 10, as confirmed in RSM Bentley Jennison (a firm) and others v Ayton [2015] EWCA Civ 1120).