The British government has resisted calls to match America's high state of alert after warnings that al Qaeda bombers might strike, playing down concerns of an immediate security threat.
The Conservative Party demanded that Prime Minister Tony Blair detail the terror threat to Britain after the United States yesterday increased security and raised the nation's alert to "High".
The US warning was prompted by Pakistan's capture of a suspected al Qaeda computer expert - Muhammad Naeem Noor Khan, also called Abu Talha - which yielded documents, computers, surveillance reports and sketches.
Newspapers said the material also indicated threats against unspecified targets in the UK.
The British government declined to follow the high-profile reaction in the United States, which moved in police armed with assault rifles to protect financial centres in New York and Washington.
A security source told Reuters the situation was reviewed daily and there were no plans to take high-visibility action.
"There is no change to the deployment. We haven't put hundreds of police officers on the streets," the source said. "If we feel we have to deploy extra officers then we will."
The Home Office said it would not discuss intelligence matters, but added the public would be told if there were an imminent threat of attack.