The Conservatives have agreed to allow the government's new anti-terror legislation to become law for eight months.

The party said it would back the Prevention of Terrorism Bill regardless of changes made to the legislation in the Lords.

But under an amendment that the Tories will propose in the Lords this week, the new legislation would expire after eight months to allow a new measure to be brought forward by whichever party wins the general election.

Labour described the move as a "major climbdown" which confirmed that the Conservatives "do not want to be on the wrong side of the argument on terror".

Charles Clarke, the home secretary, said: "If the Conservatives have a proposition they want me to to consider, I will be very happy to meet and discuss it."

David Davis, the shadow home secretary, said ministers had indicated that the terrorist risk to Britain had not changed in the past year, but the imminent general election meant that the government had to have anti-terror legislation in place.

The Tories are also to propose the establishment of a Privy Council committee to review the operation of the new laws after four months and eight months.

The legislation is due to return to the Commons next week.

Meanwhile, former judges and law lords used the debate in the House of Lords yesterday to declare that the planned anti-terror laws undermined Britain's historic legal rights.