People still drink on the tube

One of the first things that Mr Boris Johnson did as Mayor of London was to ban the consumption of alcohol on public transport. This was not a bad idea, but I wonder how well it is enforced. I was on the tube on the second day of the Notting Hill Carnival, and I witnessed a few youths happily drinking cans of Red Stripe beer. They were in high spirits, somewhat loud but not threatening at all. Should one make allowances for occasions where things are turned upside down, i.e. allow people to drink on public transport on exceptional days? The libertarian part of me thinks why not? However, the law and order side of me thinks no way! I think I will sit on the fence on this issue ...