The party's nine votes were crucial in saving the Government from a humiliating defeat in the House of Commons on Wednesday night when the unionists helped push through plans to allow terror suspects to be detained for 42 days without charge.

The DUP has confirmed it had been in discussions involving the Prime Minister right up until only 50 minutes before the critical vote, but the party firmly rejected speculation that any deals had been done.

Gordon Brown's Government pushed through the new legislation by 315 to 306 – a majority of just nine – the same number of votes held by the DUP.

The DUP said its MPs were involved in a series of last-minute meetings which involved Mr Brown before the vote. But the party rejected speculation that the meetings focused strongly on PSNI funding, the sale of Army bases, the cost of water charges or the Irish Language Act.

There was uproar in the Commons as the result of the vote was announced, with Tory and Lib Dem MPs shouting "You've been bought" at the DUP benches.

Some Labour rebels claimed the DUP had won a deal that the Government would block efforts to use the Human Embryology and Fertility Bill, currently going through Parliament, to ease abortion legislation in Northern Ireland.

However DUP MP Gregory Campbell totally rejected any suggestion that deals were done.

"We decided to vote for the extension of the pre-charge detention period after careful consideration of all the arguments and believe this is in the best interests of national security in the United Kingdom," he said.

"In any case, with some 20 to 30 rebels in the Labour Party it is clear we no longer need to threaten the Government that our votes are crucial - after last night everyone knows it.

"The DUP now holds the balance of power at Westminster and we will use it to force the pace for the benefit of Northern Ireland until the next general election, which could be two years away.

"It was an excellent result for Northern Ireland and with Gordon Brown's popularity dropping our votes are likely to become even more crucial as time goes on," he added.

The Ulster Unionist Party's MP Lady Sylvia Hermon also voted for the new legislation although SDLP Foyle MP Mark Durkan gave an impassioned last minute plea in the chamber against the new legislation, as he believed it would assist terrorists with propaganda and recruitment.

Speaking afterwards he congratulated Mr Brown on "a humiliating victory".

Accusing the DUP of having traded their votes for financial concessions, he said his party had been offered a deal by Mr Brown on Sunday. "But we told them we were not prepared to deal in civil liberties," said the SDLP leader.