At least five of the 19-strong team of suicide terrorists who hijacked four aircraft and killed thousands a week ago were reportedly trained in Britain.
Scotland Yard has been asked by the FBI to examine a list of 100 suspects and hunt down any "sleeper" cells lying dormant in the UK planning further attacks.
Dozens of homes will be raided and phone records, bank accounts, travel records and e-mails will be investigated as British special branch and anti-terrorist officers try to trace the suspects.
Scotland Yard officers have already raided an address in Brixton, south London, at the request of the FBI, but no arrests were made.
One of those being questioned by the FBI, which is organising its biggest-ever manhunt in the wake of attacks on the World Trade Center and the Pentagon, was held at Heathrow Airport having flown into the UK hours after the attacks in New York.
One of the 49 people being held by the FBI in America also lived in the UK for months, the Daily Mailclaims.
British police have arrived in New York to help the FBI and US police identify British victims of the tragedy and provide initial support to families and friends.