[Thanks to Lionel Stride of Temple Garden Chambers for providing this case summary]
The EAT (HHJ Pugsley) has handed down its decision in Heaven v Whitbread Group, which is authority for the proposition that, as the effective date of termination is a statutory construct, the date of termination in a 'conditional resignation' claim depends on what happened between the parties. Their wishes, or subsequent agreement as to a different date, are irrelevant (applying Fitzgerald v University of Kent  EWCA Civ 143).
Thus, even though the Claimant had later stated that his resignation should be effective from the date of his conditional letter of resignation, the statutory date of termination still ran from when he confirmed his intention to resign several days later. This meant that the Tribunal had erred in finding that his claim had been brought out of time.