Are you sure it was a British film and that it was a London pub? There's a scene in a noisy Sydney bar at the start is They're a Weird Mob (1969) which also ends with everyone pretending to be refined, drinking tea. But then someone suggests they break out the beer and there's a scene where they throw the beer crates to each other down the hill before the final party.
It's an Australian film but with a British director - Michael Powell
Steve