The arrests related to the terror threat to UK flights stretched across London, High Wycombe in Buckinghamshire and the West Midlands. Twenty-one people are being held in London after raids during the night. Searches are under way at a number of businesses and homes after an "unprecedented" level of surveillance. Two of those arrested under the Terrorism Act came from the Birmingham area, West Midlands police have said.
Peter Clarke, the head of Scotland Yard's anti-terrorist branch, said the investigation had involved "unprecedented" surveillance and had involved police forces in the UK and internationally. He said it was just the "very early stage" of the evidence-gathering over an alleged plot which had "global dimensions". "We have been looking at meetings, movements, travel, spending and the aspirations of a large group of people."
Houses were sealed off in Belchers Lane, in the Bordesley Green area of Birmingham. Around 20 officers, including forensic teams were at the scene.
A West Midlands Police spokesman said: "This morning two men were arrested under the Terrorism Act in Birmingham. "The arrests were part of a nationwide counter-terrorism operation co-ordinated by the Metropolitan Police Counter-Terrorist Branch." The spokesman said no firearms had been involved and the men were still in custody.
In High Wycombe, Buckinghamshire, an address in Walton Drive was among those raided and at least one person was arrested. The majority of arrests were in London, but the location of these has not been specified.