It is highly likely that terrorists will attempt to mount an attack in Britain over the holiday period, the country's top law and order official said on Sunday.
Home Secretary John Reid said the threat of an attack in Britain remained severe, but gave no details of any possible plots.
"The threat in this country is very high indeed," Reid told the television program GMTV on Sunday. "We know that the number of conspiracies of a major type are in the tens - 30 or round about that."
The government's threat status was raised to "severe" - the second-highest level - in August, when an alleged plot to down trans-Atlantic jetliners with liquid explosives was uncovered. Reid said the level meant "it is highly likely there will be a terrorist attempt."
Reid said that he did not believe an attack was inevitable, but said that terrorists only have to "get through" once.
"Our security services have to be successful on every occasion to prevent that happening," Reid said.
In November, Dame Eliza Manningham-Buller - who heads MI5, Britain's domestic spy service - said authorities were tracking almost 30 terrorist plots involving 1,600 suspects and that her agency had foiled five major plots since the July 2005 transit bomb attacks in London.