Northern Ireland politicians may hold the balance of power at Westminster next month.

Cabinet ministers remain divided over the need to force through new laws to extend the maximum detention of suspected terror suspects from 28 to 42 days without charge - a month before the Government could face defeat by up to 30 votes in the Commons over the issue.

The only success Labour whips appear to have had is to persuade Northern Ireland's Democratic Unionist Party (DUP) - which has just elected its new leader - to possibly abstain or vote with the government.

The DUP - and its leader elect, Peter Robinson - voted against 90-day detention last time, and their role is being seen as crucial to the Bill's success this time around.

However, the split goes deep as even Jack Straw, the Justice Secretary, has privately expressed doubts about Gordon Brown's determination to insist on 42 days because he fears it could lead to further tensions in the Muslim community and paradoxically could lead to less intelligence being supplied to the authorities from Muslim sources.

However, Mr Straw, who has a big Muslim community in his Blackburn constituency, will be publicly backing the policy and voting for the Government - but this does not mean he agrees with the necessity to do it.

He has remained conspicuously silent in public in pushing the policy.

His view is at odds with Jacqui Smith, the Home Secretary, who has said that British intelligence was pursuing 30 different plots involving the tracking of 2,000 people in 200 networks.

But critics pointed out that these figures were no higher than two years ago and did not appear to contain new information.

Smith, who is keen to convince wavering Labour backbenchers to vote for the measure, said: "We can't wait for an attack to succeed and then rush in new powers.

"We've got to stay ahead. When we extended the period from 14 to 28 days people said 'there's no need for this, it's not necessary. You'll never need to use it'. Well, we did.

"The number of international investigations is greater than before. Each time a plot is uncovered the terrorists learn and they develop.

"That is why there is a massive increase in the way they are using technology and encrypting evidence. It takes time to get the evidence you need to charge somebody," she said.

Under the proposals, which have been revised to include some safeguards, the Home Secretary would be able to immediately extend the limit to 42 days if a joint report by a chief constable and the Director of Public Prosecutions backed the move.

Liberal Democrat and Tory MPs are united against the measure.

David Davis, the Shadow Home Secretary, said: "This policy is friendless even among members of the cabinet. It is a sign of desperation that the home secretary is citing as 'new' evidence details given in a speech by the head of MI5 five months ago.

"In fact, Jonathan Evans did not even mention pre-charge detention when setting out the counter-terrorism challenges we face - either in public or private briefings," he said.

(BMcC)