British Home Secretary Jacqui Smith said a lack of data about potential terrorist attacks led to the threat level's reduction from critical, The Telegraph reported.

"There remains a serious and real threat against the United Kingdom and I would again ask that the public remain vigilant," Smith said.

The threat level reduction comes as British intelligence officials released new information on last week's failed car bombings in England and Scotland.

Intelligence experts in Britain said they had no reason to believe the doctors tied to the terrorist attacks were recruited by al-Qaida before joining the National Health Service.

That news contradicts a report Tuesday from U.S. intelligence sources that said the doctors were recruited by the terrorist organization three years ago in Iraq, the British newspaper said.