In a shock announcement, the shadow home secretary resigned as MP for Howden and Haltemprice to force a by-election on the controversial issue.

He said he wanted to "take a stand" against the Government's "slow strangulation of fundamental British freedoms".

But the move was greeted with anger and frustration by the Tory leadership, which was given only a few hours notice and clearly did not sanction it.

Mr Davis admitted David Cameron had warned him that resigning was "very risky", but insisted his mind had already been made up after a ferocious Government whipping operation secured narrow victory in the key terror vote.

The 59-year-old insisted he did not believe his actions would damage the Tories, and stressed there was no split with Mr Cameron on the 42-day issue.

But Mr Cameron's fears that his party's good progress could be derailed were in danger of being realised as Labour rushed to capitalise on the chaos.

Home Secretary Jacqui Smith accused the Conservatives of being in "total disarray", and said they needed to "come clean" over what had happened.

Frontbencher Dominic Grieve, who was immediately appointed to replace Mr Davis in the home affairs brief, dismissed speculation about a policy split as "fantasy" and insisted the Opposition was still determined to repeal 42-days if it becomes law.

But he conceded it was too early to tell whether the resignation - by a man regarded as one of the Tories' most effective operators - would help or harm the party.