Home Secretary Jacqui Smith dropped plans to extend to 42 days the time terror suspects could be detained before being charged.

In an emergency statement to the House of Commons after the proposals were defeated in the Lords, she said a separate Bill which included the measures was written and ready to be made law – if it was needed.

Measures in the Counter Terrorism Bill to add two weeks to the pre-charge detention limit were defeated by a crushing 191 votes in the Lords, including those of former Labour Lord Chancellors Lord Falconer and Lord Irvine. These will now be dropped from the Bill.

Ms Smith attacked opponents of the proposals, saying: "Some may take the security of the British people lightly. I do not."

Ms Smith said she was not prepared to leave the British people unprotected against the terror threat. She accused critics of "being prepared to ignore the terrorist threat for fear of taking a tough but necessary decision".

With Prime Minister Gordon Brown sitting behind her, Ms Smith said: "I do not believe, as some clearly do, that it is enough to simply cross our fingers and hope for the best.

"Because when it comes to national security, there are certain risks I'm not prepared to take.

"I am not prepared to risk leaving the British people without the protection they need."

Ministers will hope the presentation of the new Bill will give them a degree of political cover as they walk away from what was a major plank of their counter-terror policy.

They were left with little choice but to ditch the plans when faced with the prospect of a bruising return to the Commons. The Government's majority was slashed to nine in an earlier vote on the 42-day measure this summer.

The measure squeezed through in June despite more than 30 Labour rebels voting with the Opposition, thanks to the support of Democratic Unionist MPs.

Liberal Democrat leader Nick Clegg said the move was a "victory for civil liberties" and the new Bill a "fig leaf".

He said: "The decision to prepare emergency legislation instead is merely a fig leaf which does little to disguise their defeat.

"The push for 42 days detention was more about Ministers posturing and looking tough than it ever was about fighting terrorism."

Former Tory Shadow Home Secretary David Davis, who resigned his seat after the Commons vote over the 42 days issue, said it was a "spectacular climbdown".

The Haltemprice and Howden MP said: "This demonstrates only too clearly that this measure has always been all about politics."

In the Lords, opposition to the Bill was led by former chief constable Lord Dear, who said there was "no evidence to date" that the existing 28-day limit was too low.

He said: "This attempt to appear tough on terrorism, I believe, is a shabby charade which is unworthy of a democratic process and we should reject it."

To extend the law would "almost certainly give ammunition to those who seek to justify acts of terrorism against us", he said.

Labour former Attorney General Lord Goldsmith, one of the most vocal senior critics of the 42-day proposal, last night welcomed the climbdown.

"It is absolutely the right decision not to pursue this any further. It was not only unnecessary but dangerous," he said.