Britain faces a severe risk of another terrorist attack, a Cabinet minister said Monday as he unveiled a system for sharing threat assessments with the public for the first time.

The new terror alert status system is based on a U.S. Department of Homeland Security model. It will take effect Aug. 1, British Home Secretary John Reid said in a speech to the House of Commons.

The system will rate the threat as low, moderate, substantial, severe or critical.

"Critical" would indicate strong intelligence of an expected imminent attack. The threat assessment was for the country as a whole and would not indicate the threat to any locality.

"This is not an exact science. It involves human judgment," Reid said days after the first anniversary of the attacks on London's transport system in which 52 commuters and four bombers died.

The U.S. alert system uses a color-coded five-point scale to gauge the threat level ranging from green for low to red for severe.

The previous British system was strongly criticized by Parliament's Intelligence and Security Committee in a report issued in May. It found that Britain's threat level had been reduced from "severe general" to "substantial" immediately before the attack, but said the decision was "not unreasonable" based on the intelligence available.

The report called for better public access to information about Britain's alert status.

"There is a growing recognition among ministers and within the Home Office that the public have a right to know about we are doing, even more so since July 7," a Home Office spokeswoman said on condition of anonymity, in line with department policy.

Also on Monday, the government dropped an idea Prime Minister Tony Blair said officials would consider shortly after the London bombings last year _ limiting how long extradition proceedings could continue for terror suspects sought by other countries.

The Home Office said experts had decided such a limit was not feasible, since it could give suspects grounds for challenging their extradition.

Blair had said cases in which extradition hearings drag on for years were completely unacceptable.