Boris Johnson’s alcohol ban on the Tube is impossible to enforce, unions claim
...staff working for Transport for London and British Transport Police will not have the power to fine passengers, and officials admitted that there would not be regular patrols of carriages.
Instead, Mr Johnson will rely on a “cultural shift” and self-policing to bring a halt to drinking in the same way that passengers help to enforce the Tube’s no-smoking rules.
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The ban will be brought into force by changing the conditions of carriage on London transport, but until it is enshrined in a bylaw, which the mayor said would take about a year, there is no punishment available to transport staff except for ejection.
http://www.timesonline.co.uk/tol/news/uk/crime/article3890097.ece