As of midnight last night, it is illegal to drink on public transport. Obviously, one was never allowed to drink on the subway in New York, but here it was always legal until the newly-elected mayor decided to clean up London's public transportation system. To "celebrate" the ban, thousands of people decided to host a party on the Circle Line, the yellow subway line that circles inner London; people were going to hang out on the train, drinking, riding around in circles until midnight.
The tube in London does not run 24-hrs like it does in New York, so the party had to end at 12:30 when the last trains departed. However, the celebration apparently got messy and tube stations had to be closed because of the melee. CNN has a good run-down of the ridiculousness here.
Thank god I stayed at Ashley's... if I had tried to go home on the train last night, I would have gotten caught in that nonsense, and I don't suffer puke on a subway quite well.