The arrests on Tuesday came a day after the US raised its terror-alert amid growing fears the al-Qaida was planning to attack financial centres in the country.
"The men have been arrested on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism," a British police statement said.
Britain had resisted calls to match the US' high state of alert - prompted by the capture of a suspected al-Qaida computer expert in Pakistan - which yielded documents, computers, surveillance reports and sketches.
"The men have been arrested on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism"
British newspapers said the materials also indicated threats against unspecified targets in UK.
A police spokesman, however, declined to say if there was a link between intelligence from the arrest and the raids.
British media reported that some of those arrested were British citizens and all of Asian origin.
The police said the operation was part of extensive inquiries by police and the security service into alleged international terrorism.
The media said the detainees had been under surveillance for a while and speculated police might have acted more quickly than originally planned after the arrest of the computer expert.