Londoners began cleaning up their city after a third night of riots on Tuesday, aided by a Twitter and Facebook campaign which rallied people to the most damaged areas.

Fires broke out across the capital on Monday night as looters smashed up and set ablaze buildings, shops and cars, while violence also broke out in the cities of Birmingham, Liverpool and Bristol.

In Peckham in southeast London, about 20 members of the community arrived on the high street on Tuesday morning armed with dustpans and brushes to offer small businesses help in cleaning up their shops which had been smashed in.

"I was devastated when I saw what happened last night. I was really angry so I thought I'd channel my anger in a constructive way," said one woman in her 20s.

"We have never met each other before, we just spoke on Twitter this morning. Twitter can be used for good."

An online campaign, Clean Up London, (@Riotcleanup) had 27,500 followers on Twitter by mid-morning on Tuesday, as it instructed people to congregate to remove the glass and bricks strewn across the streets of the city.

"Moving from Lewisham towards Catford now as Lewisham seems to be pretty cleaned up by now," said one post, referring to areas in southeast London, while another added: "Hackney is clean too. This city is resilient."

Similar messages were sent out about Liverpool, calling for help to clean-up a "bombed out church" in the northwestern city.

The Association of British Insurers estimated the damage caused by the riots across Britain as "tens of millions of pounds".