A "lock-in" is when a pub owner lets drinkers stay in the pub after the legal closing time, on the theory that once the doors are locked, it becomes a private party rather than a pub. Patrons may put money behind the bar before official closing time, and redeem their drinks during the lock-in so no drinks are technically sold after closing time. The origin of the British lock-in was a reaction to <answer>1915</answer> changes in the licensing laws in England and Wales, which curtailed opening hours to stop factory workers from turning up drunk and harming the war effort. Since <answer>1915</answer>, the UK licensing laws had changed very little, with comparatively early closing times. The tradition of the lock-in therefore remained. Since the implementation of Licensing Act 2003, premises in England and Wales may apply to extend their opening hours beyond 11 pm, allowing round-the-clock drinking and removing much of the need for lock-ins. Since the smoking ban, some establishments operated a lock-in during which the remaining patrons could smoke without repercussions but, unlike drinking lock-ins, allowing smoking in a pub was still a prosecutable offence.
A law of what year prompted the existence of the "lock-in"?
1915