Drinking on public transport in London

This came up on something I was reading with a photo of people enjoying some drinks. We did quite a lot of travelling on public transport in London before 2008 and I don't ever recall people drinking let alone partying. We came back to our lodging after seeing a play or some event so were on transit in the evening. "On 7 May 2008, the newly elected Mayor of London Boris Johnson announced that the drinking of alcohol would be banned on all public transport services run by Transport for London from 1 June." I do remember people drinking and eating on trains in France and other public places but not on public transport like the subway. I don't know what the laws were.