Boris Johnson has called on the police to "get medieval" on rioters as he backed proposals for the Metropolitan police to be allowed to use water cannon on future protests.
The mayor of London said the police needed to "come down much harder" than they did in the London riots in 2011.
"When you have something kicking off like that you do not let it get under control, you get medieval immediately on those people and you come down much harder and you do not allow a mentality to arise of sheer wanton criminality, which is what you saw take place," he told the London Assembly.
Johnson has previously opposed the introduction of water cannon, which have been responsible for inflicting serious injuries in other countries, saying that he did not want an "arms race" with protesters.
However he said he had changed his mind as it was "very difficult as policy makers to say no" when the police asked him for them
Johnson's U-turn follows a report by the Association of Chief Police Officers which claimed that the weapons would have been useful on three occasions in the past ten years.
It highlighted the London riots in 2011, the student riots at Millbank in 2010 and the Countryside Alliance protests in 2004.
Johnson said he would have opposed their use during the student riots as "counter productive" but conceded that any operational decision on their use would not have been taken by him.
He insisted that water cannon would be "very, very rarely used if ever."
Johnson wants Theresa May to allow the police to use water cannon by this summer.
Assistant Commsioner Mark Rowley admitted that the police had no specific intelligence that trouble was expected by then but insisted that "we simply want it as soon as possible."
He also conceded that water cannon would have been of limited use in the 2011 riots.
"Most of the disorder in the riots it would not have been a sensible tactic in," he told the Assembly.
"We are not presenting it as a silver bullet for all serious disorder. That is not what water cannon is."
Labour today urged Johnson to think again about introducing water cannon.
"I’m deeply concerned that the Mayor is rushing the purchase of water cannon without a proper public debate," Labour's London Assembly policing spokesperson Joanne McCartney said.
"Since 2010 we’ve lost 2,900 police officers and 2,370 PCSOs. Water cannon are no substitute for a visible uniformed presence on our streets.
"Such a monumental shift in policing needs a proper public debate."