Violent drunks should be allowed to stay out of prison as long as they “stay off the booze”, the London Mayor has said.

Boris Johnson said hospital accident and emergency departments are full of “the victims and perpetrators of drink-fuelled violence” and, apart from prison, there are very few tools “to stop the drunken thug from going out and doing it again”.

Instead, anyone convicted of alcohol-related violence should be allowed to stay out of prison if they attend a police station twice a day to take a breathalyser test and prove they are sober, he said.

Writing in The Daily Telegraph, he said a similar scheme in South Dakota had cut the prison population by 14%.

“We need to look much harder at the role of alcohol in crime, and above all in violent crime,” he said.

“That is a big financial saving – and all from finding a way to keep the drunken thugs sober.”

He went on: “You simply require the individual to take a breath-test twice a day. You make it a condition of his (and it is normally his) parole that he must report twice a day to a police station and prove that he has not been drinking; otherwise he is arrested and locked up.

“And it doesn’t cost the state a thing, because you make sure that the – relatively low – cost of the breathalyser test is met by the offender.”

The programme is both cheap and “has real teeth”, he said, but similar proposals in England and Wales had been met with “a certain amount of what I will politely call bureaucratic resistance”.

Mr Johnson added: “If we won’t lock them up, and we want to cut drunken violence, then sobriety tests must be part of the answer. We need to pilot the scheme now.”