TONY Blair faces a nail-biting showdown with the House of Lords today to pass fresh anti-terror laws before ten al Qaida suspects must be released from prison.

The Prime Minister made a series of concessions last night on his plans for control orders for suspects, to win the support of his rebellious backbenchers and send the Prevention of Terrorism Bill back to the Lords.

But he refused to give ground on Tory and Liberal Democrat demands for a higher standard of proof and a "sunset clause", which would mean the legislation would automatically lapse in November.

Instead, in stormy Commons clashes, Mr Blair dared Conservative leader Michael Howard to continue to oppose powers he insisted had been requested by both the police and security services.

The stand-off raised the prospect - however unlikely - of the ten foreign terror suspects locked up in London's Belmarsh Prison for the past three years walking free on Monday.

Previous anti-terror laws, introduced in the wake of the September 11 atrocities, lapse on Monday. Ministers insist they cannot be renewed because they have been declared illegal by the Law Lords.

At Prime Minister's questions, Mr Howard made the extraordinary claim that Mr Blair wanted the Bill to fail - so he could condemn the Tories as "soft on terror" in the coming election campaign.

Mr Howard said: "You want to pretend that you are the only one who is tough on terrorism. Isn't it a dreadful measure from a desperate prime minister and shouldn't you be thoroughly ashamed of yourself?"

In reply, Mr Blair said: "The shame will lie with the Conservative party - faced with legislation to prevent terrorism, faced with legislation advised on us by our police and security services - that are going to vote against it.

"If they want to vote against it, let them. We will be content, ultimately, to have the verdict of the country on it."

Last week, Labour's 161-seat majority was cut to 14 when 60 rebel backbenchers demanded that a judge - rather than Home Secretary Charles Clarke - impose all control orders.

Yesterday, Mr Clarke backed down on that issue - allowing the Government to win the vote with a comfortable 108 majority - although he can still impose the orders in an emergency.

The Home Secretary also agreed to an annual review of the legislation, but continued to insist that a sunset clause with a November timetable was unnecessary.

The closest vote, a Government majority of 89, came over the issue of the standard of proof required for imposing the lesser control orders - those stopping short of house arrest.

The Government insists the orders must be made on the basis of "reasonable suspicion", but the Lords has demanded a higher standard of "balance of probabilities".

Redcar MP Vera Baird was among the Labour rebels who switched to supporting the Government after she said she was hugely cheered by the legislation's changes.

But, last night, the Government was expected to have to give further ground over the sunset clause or the standard of proof to get the Bill through before tonight, when MPs leave Westminster for the week.

Despite his insistence that the Belmarsh prisoners would have to walk free, Mr Clarke has tabled an order to extend the existing powers for nine months - in case the Bill is lost.

If the legislation is passed, the foreign suspects will be released under control orders restricting their movements and their use of the telephone and the Internet and allowing them to be tagged.