HMDS2752 - When a Stamp May Be Applied: Subject to certain exceptions, relevant products must bear a duty stamp at the time that they pass a UK duty point

Traders are free to apply stamps at any point between bottling and removal to home use on payment of duty. In practice, this has different implications for different types of trader. But for label stamps, in all cases, the label stamp is affixed to the retail container at the time the label is applied to the bottle.