Mr Mills, aged 56, said he had fallen over while carrying a heavy load of papers, a briefcase, and a computer. "I certainly was not drunk," he insisted.
However, a spokesman for the Metropolitan Police said he could say what he liked. "The man was found slumped in a doorway. He was arrested for being drunk and he was given a drunkenness warning. Obviously, he can claim he wasn't drunk. If I was arrested for robbing a bank I could claim I didn't do it. But we believe he was drunk."
Mr Mills, MP for his West Midlands constituency since 1979, has campaigned against drink-driving in the past. He was picked up from the pavement in Great Smith Street shortly before 1am and taken to Charing Cross police station. He was released at 5.15am after being given a "drunkenness warning".
A Metropolitan Police Federation representative said the officers involved would not have made a mistake: "He wouldn't have got a drunkenness warning unless he'd been drunk."