Britain has lowered its national security level from its highest level, "critical" to "severe," indicating that authorities no longer believe a terrorist attack is imminent.

Home Secretary Jacqui Smith said the action does not mean the threat of terrorism is gone and urged the public to stay vigilant.

The decision to lower the terror threat one level came after the detention of eight people following car bombing attempts in London and Glasgow last week.

British authorities say all eight are doctors or worked for the country's national health service.

Britain's Prime Minister Gordon Brown is seen after a meeting of the government's top emergency committee Cobra, 29 Jun 2007

Earlier, British Prime Minister Gordon Brown told parliament authorities will expand background checks on immigrants entering the country to fill skilled jobs, including medical personnel.

Also Wednesday, a senior British cleric said that last April he met in Jordan with an unnamed al-Qaida leader who apparently warned him of attacks by doctors. Canon Andrew White said the al-Qaida official told him that "those who cure you are going to kill you." He said meeting the man was like meeting the devil. White runs an Anglican church in Baghdad. He said he passed the information to the British Foreign Office, which denies receiving the warning.

Some information for this report was provided by AP.