Their default defence. Think it has been successfully challenged in respect of premium services such as “Special Delivery”
Thread below is a good read, Ryan. Gives you some idea of the lengths Royal Mail will go to to make any legal claim as difficult as possible. Laughable (in respect of RM’s attempt at a complex defence) for the relatively tiny sum but the Claimant was successful.
https://www.consumeractiongroup.co.u...-to-court-won/