New anti-terror powers would only be used in the face of a "grave exceptional" threat to the UK, the Home Secretary has pledged in a bid to win over Labour rebels.
Jacqui Smith made public a series of concessions on 42-day detention without charge which she set out to backbenchers threatening a damaging revolt.
She said the time for which the police could use the power would be halved to 30 days and MPs would have to approve them being invoked within a week rather than a month.
It raises the prospect of Parliament being recalled for an emergency session should a major threat be uncovered during one of its long holiday periods.
The changes won over some of the 50 potential backbench rebels although Downing Street insisted victory was "not in the bag".
