Green’s Dictionary of Slang

drinker n.

1. an after-hours or unlicensed drinking club.

[UK]B. Hill Boss of Britain’s Underworld 124: The Stoprk Club was both a speiler [sic] and a drinker.
[UK]G.F. Newman Sir, You Bastard 194: Some afternoons [...] were best spent in a drinker.
[UK](con. 1980s) N. ‘Razor’ Smith A Few Kind Words and a Loaded Gun 285: If you go mob-handed to an after-hours drinker and try your luck starting fights with strangers, how can you turn around and cry ‘copper’ when you come unstuck.
[UK]T. Black Artefacts of the Dead [ebook] They’re going to check a few hacks’ drinkers.

2. a public house.

[UK]A. Payne ‘The Dessert Song’ in Minder [TV script] 16: Terry down the drinker wrestling Irishmen?
[UK]M. Amis London Fields 336: With a shudder, he’d rear up, fling on a mack and, Keith assumed, slope off down the drinker.
[UK]T. Black Gutted 167: There was a nice-looking little drinker over the road, gas lamps hanging alongside the Younger’s Tartan Special gadgie.
[US]T. Black Ringer [ebook] n.p.: I [...] heads out for a pint down the drinker.