Beyond Selidor

Drinking on the underground in London is not allowed, but as far as I'm aware, there is no rule against it on long-haul trains (and indeed most largeish train stations have shops selling, among other things, alcohol, and trains that have restaurant cars in the UK and elsewhere in Europe usually sell beer and small bottles of wine). These specific kinds of groups (women sharing bottles of sparkling wine, and men with cans of beer) are so common on Saturdays that it's almost a cliché — as demonstrated by the other comments here from British people. I also always see these exact groups of drinking people every time I catch a train on a Saturday in Germany, and elsewhere in continental Europe.