Britain reveals new terror threats

Police had swooped on key suspects on Thursday over an alleged plot to wreak mass murder by smuggling liquids in hand baggage onto US-bound planes to assemble into bombs.

Questioned about how many terrorist attacks had been stopped since the July 2005 London bombings, Home Secretary John Reid told the BBC News 24 television channel on Sunday: "I can tell you that at least four major plots have been thwarted."

Reid said that the plots would have led to significant loss of life and indicated that up to two dozen terror investigations were currently being pursued, confirming reports that police were hunting that number of terror cells in Britain.

"I'm not going to confirm an exact number but I wouldn't deny that that would indicate the number of major conspiracies that we are trying to look at," Reid said.

Regarding Thursday's terror raids, a Metropolitan Police spokeswoman told AFP on Sunday that enquiries were ongoing and searches continuing while 23 suspects remained in custody.

Reid added: "We think we have the main suspects in this particular plot."

"I have to be honest and say on the basis of what we know, there could be others out there ... so the threat of a terrorist attack in the UK is still very substantial."

Britain on Thursday upped its security alert to "critical" -- the highest of five levels -- from "severe," where it had been since security was relaxed in the weeks after the London transport attacks of July 2005, which killed 56 people.

Last week's news has caused air travel chaos around the world, especially in Britain. Stringent security checks were introduced, reviving memories of the September 11 attacks in the United States in 2001.

British airports operator BAA argues that the measures -- including body checks and the banning of hand luggage -- were not sustainable, while all airlines have struggled to cope with the new demands.