I wouldn't worry too much; Mr. Blair and his government are big on talk and short on action. This proposal will either die or suffer the "Reid Effect".
Labour will fail to understand that banning alcohol on public transport will not stop its use for the simple reason that the Labour government will not provide the resources to enforce the ban. This has been the experience of very good anti-litter and other environmental legislation - no back up (analogous to the Government's lack of back bone).
Labour - a strange bunch of socialists