Manchester could have been spared the August riots if police in London had acted sooner, according to the city's chief constable.
Greater Manchester Police chief Peter Fahy told BBC Panorama that copycat violence broke out after people saw rioters were "getting away with" their behaviour in the capital.
Mr Fahy said: "A certain group of people saw what was happening in London and decided they seemed to be getting away with it.
"The authorities weren't in control and they decided they wanted their opportunity."
He told the programme he did not regret the decision to send 100 officers from Greater Manchester Police to help deal with the situation in London.
"We knew what was absolutely critical was that there needed to be control of London. Because that was just creating more and more copycat violence up here."
Mr Fahy added: "I think you'd have to say with hindsight if London had been under control sooner we probably would not have faced the problems in Manchester."
Manchester Police have arrested more than 350 people in connection with the riots.
Mr Fahy told the programme the force is still tracking down hundreds of suspects from at least 300 crime scenes.
Early findings from the Metropolitan Police's review into its policing of the riots concluded that too few officers were deployed on the first night of violence.
The disturbances began in Tottenham, north London, on Saturday August 6 in response to the fatal police shooting of father-of-four Mark Duggan, 29, and spread throughout the capital and then across England.
Scotland Yard said it had about 3,000 policemen and women on duty across London on the first night of the riots, and it deployed 480 trained public order officers to the disorder in Tottenham.
By Monday August 8, by far the worst night of violence in the capital, there were around 6,000 officers on duty, of whom 1,900 had specialist public order training.
The Met Police review said the scale of the disorder and the speed with which it spread to 22 of London's 32 boroughs on a single night made it "unprecedented".
The force also said it was re-examining how it draws intelligence from social media like Twitter and Facebook.
The riots in the capital followed the resignations in July of the then Met Commissioner Sir Paul Stephenson and Assistant Commissioner John Yates in the wake of the phone hacking scandal.
Paul McKeever, chairman of the Police Federation of England and Wales, defended the actions of the Met.
"I think any police force in the world would have found it extremely difficult to cope with the rapidly escalating violence that we experienced in London," he said.
He added: "Peter Fahy is a man who is held in high regard and respect and somebody we should listen to, but the officers in London did a magnificent job, putting their lives on the line to protect their communities.
"It took 16,000 officers to actually get the riots under control and there were officers from all around the country. I don't think anybody expected to see the disorder escalate so rapidly and become so widespread.
"I am sure it is not Peter Fahy's intention to criticise officers who policed the riots in any shape or form. I would suppose that he is trying to make a serious statement.
"More than 250 officers were injured during the riots and many of them are still suffering as a result of these injuries. Our thoughts are with them and they should be commended for their actions."