The Home Affairs Committee has concluded that the government must not block social networking sites such as Twitter or Facebook - or messaging services such as BlackBerry Messenger - should riots reoccur in the UK.

The recommendation came even though the committee said social media played a part in enabling the summer riots to take place. Rioters used social media to co-ordinate trouble, but "television also played a part", the committee said, and it "strongly recommended" letting social media continue to run - because its role in spreading trouble was "limited". Social networking sites had also aided police in reassuring people, the committee noted.

Acting commissioner Tim Godwin of the Metropolitan Police agreed in evidence to the committee that it would be a "negative" move to turn off the services.

While politicians denounced the role of social networking sites in the aftermath of the riots, the companies themselves gave a more nuanced picture on how much their networks had been used.

Stephen Bates, the UK and Ireland managing director of Research in Motion, which produces the BlackBerry device and runs BBM, said: "There is no dispute that social media was used for malicious purposes."

But Richard Allan, director of policy at Facebook, said that the site had only been used for the disturbances in "a handful of cases".

Alexander Macgillivray, general counsel at Twitter, was asked whether that site was used for organising the trouble. "We haven't seen that, at least I have not seen it yet in this particular case," he said.

The Home Affairs Committee concluded overall that the police had underestimated the magnitude of the riots, and had taken too long to deploy enough officers on the street.

The authorities had eventually made good use of social media to inform the public of their actions - but there needed to be a much better communications strategy between forces, the committee said.

"All police forces should have a communication strategy in place, so that if it is decided that there is a credible threat of severe public disorder, all business in the affected area are given early and consistent advice about what action they should take," said the committee. "This did not happen in August."

In spite of a need for better collaboration and communication, the committee said, the riots in different cities could not be grouped into one category. But it added: "The single most important reason why the disorder spread was the perception, relayed by television as well as social media, that in some areas the police had lost control of the streets."

Keith Vaz MP, the committee's chairman, said: "Individual police officers acted with great bravery, and we commend them for their actions. However, in London and other areas, in contrast with the effectiveness of police responses in some towns and cities, there was a failure of police tactics. This situation might have been avoided had police appreciated the magnitude of the task.

"We urgently require a rapid improvement in police training to deal with public disorder."