Rioting has spread across London on a third night of violence, with unrest flaring in other English cities.
An extra 1,700 police officers were deployed in London, where shops were looted and buildings were set alight.
Birmingham, Liverpool, Nottingham and Bristol also saw violence.
The prime minister has returned early from his holiday to discuss the unrest, which first flared on Saturday after a peaceful protest in Tottenham over the fatal shooting of a man by police.
At least 400 people have been arrested following a wave of "copycat criminal activity" across London over the past three days, the Met Police said. More than 69 people have been charged with various offences.
Three people are being questioned on suspicion of attempted murder after a police officer was injured by a car in Brent, north-west London, while trying to stop suspected looters.
Met Deputy Assistant Commissioner Steven Kavanagh said it was a "shocking and appalling morning for London to wake up to".
"The Met was stretched beyond belief in a way that it has never experienced before," he told BBC Breakfast.
When asked at what stage he would consider bringing in the Army, he responded by saying "all options are being considered".
On
Twitter, Scotland Yard said: "In the next 24 hours there will be 13,000 police officers on duty in London."
