Britain's biggest police force has admitted it did not have enough officers available on the first night of the August riots, and reinforcements took too long to arrive.
The Metropolitan Police 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".
Releasing early findings from its ongoing review of how it policed the looting and violence, the force said it was re-examining how it draws intelligence from social media like Twitter and Facebook.
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 noted that the number of officers sent to Tottenham on August 6 met the levels set out in its pre-existing plan for tackling disorder, but admitted this was inadequate.
"With hindsight the numbers were not enough and they did not arrive quickly enough," it said in a preliminary report into the riots.
The force is now changing its procedures so public order-trained officers can be mobilised more quickly.
Scotland Yard highlighted the difficulty of keeping on top of the huge number of posts about the disturbances made on social media.
"The combination of volume and speed of information at unprecedented levels posed a significant challenge to policing during the height of disorder," the report said.
"The MPS (Metropolitan Police Service) is reviewing systems to co-ordinate, assess and prioritise social media content for intelligence purposes."
Responding to criticisms that some officers stood by while looters ran amok, the force said it had found no evidence that senior commanders ordered police on the ground not to make arrests if offences were taking place.
There were calls from some quarters for officers to use water cannon on the rioters. The Met said it would review the cost of making the weapons available but stressed there were limitations to how they can be used.
The report also noted that baton rounds, which were authorised but not used during the disorder, might have been deployed if more specialist teams were available over a wider area.
Scotland Yard Assistant Commissioner Lynne Owens said: "Thoroughly reviewing disorder that touched almost every part of London was always going to be a significant task and we are progressing this as quickly as we can.
"We are committed to being as open as possible so that we, our partners and the public can properly understand what worked, what didn't and what we need to do differently.
"Today's report provides some high-level emerging findings and we will publish more detailed findings as the review further progresses."
The Metropolitan Police Authority, which oversees Scotland Yard, has received 3,844 claims for compensation under the Riot Damages Act from people affected by the disorder.
The authority aims to recover all its costs, estimated at between £200 million and £300 million, from the Home Office.