Mr Brown revealed the review as eight people with links to the health service were held over car bomb attacks on London and Glasgow.

The news came as Home Secretary Jacqui Smith announced the national terror threat level had been reduced from critical to severe.

Speaking during his first session of Prime Minister's Questions in the Commons, Mr Brown announced the Government will take fresh steps to counter terrorism.

These will include the expansion worldwide of a "watch list" of potential terrorists to help warn other countries.

And new agreements would be signed with countries around the world to ensure a co-ordinated response to the terrorist threat.

Lord West, the new terrorism minister, will be responsible for the review of recruitment in the NHS .

The Prime Minister's comments came as detectives continued to question six people held at Paddington Green police station in central London. Five men have links to the health service either as doctors or trainee doctors, while the sixth person, a woman, is a laboratory researcher.

Another doctor is being quizzed by officers in Australia while the eighth person remains in a critical condition in hospital in Glasgow with severe burns. Earlier, it emerged that some of the eight suspects were known to MI5 through links with others under surveillance.

There was controversy earlier this year when it emerged that the ringleader of the July 7 attacks had also crossed the radar of the security services.