Boris Johnson has suggested that social media sites should be kept open to provide intelligence for police during periods of public disorder, despite calls by the government to block websites or ban known criminals following the riots that spread across the country earlier this month.

The London mayor’s comments come ahead of a summit held by the home secretary, Theresa May, on Thursday, in which representatives from Facebook, Twitter and Research In Motion, the Canadian maker of the BlackBerry mobile device, will meet police to discuss how social networking sites were used to plan riots.

Department officials said the agenda would include how to stop people plotting violence on social networks and what action could be taken to prevent access to those networks by known criminals involved in disorder.