"I'VE BEEN IN THE PUB AND FEEL DRUNK. CAN I VOTE?

Yes. Polling station staff cannot refuse a voter simply because they are drunk or under the influence of drugs. However, if the presiding officer suspects you are incapable of voting you will be asked a series of questions to determine whether you are up to the task of casting your ballot. If the voter cannot answer satisfactorily they will be told to come back when they've sobered up."

http://news.bbc.co.uk/1/hi/uk_politics/election_2010/8661984.stm