Last-minute availability in London theatre is not a single channel - it is a handful of routes that overlap. This page summarises the ones that consistently work.
TKTS Leicester Square
Official same-day and next-day tickets. Best for plays and musicals that have not sold out.
Show apps
Several long-running musicals release blocks of last-minute tickets through their own apps or TodayTix the morning of a show.
The venue box office
Returns, day seats and unsold premium tickets are typically routed through the venue box office in person. Worth a fifteen-minute walk if you are already in town.
Off-West End
The Old Vic, the Bridge, the Almeida, the Donmar, the National and the Royal Court usually have last-minute returns through their websites and front-of-house ticket desks.