The DUP will support Labour's bid to push the Bill through the Lords.

Although the legislation is likely to be defeated in the upper house, the party's three peers said they would be voting in line with their MPs, whose crucial nine members helped the controversial Bill through the House of Commons.

The Bill would mean police have two extra weeks to question someone arrested on suspicion of a terrorism offence before they were required to be charged or released.

The DUP's Lord Browne said: "Intelligence gathering in the 21st century is a complex and often international task involving networks of individuals and computers. This clearly requires a longer timeframe in order to carry out this task successfully.

"There have been clear indications of the need for this kind of proposal by those involved in the intelligence gathering required when tackling today's international terrorist networks.

"It is important that the law does change to reflect the circumstances we are unfortunately faced with today."

The first debate on the law will be held in the Lords tonight and will include the DUP's Lord Morrow, Lord Browne and Ian Paisley's wife Baroness Paisley.

However, Ulster Unionists will vote against the Bill.

The News Letter understands that Lord Laird, Lord Maginnis and Lord Rogan will join with other peers to kick the legislation out.

This is despite the fact that the party's sole MP, Lady Sylvia Hermon, backed the Government plans in the House of Commons last month.

Speaking last night, Lord Laird said people needed to think calmly and rationally about what was being suggested by Gordon Brown.

"We are talking about locking up potentially innocent people for 42 days," he said.

"It could be your father or brother. The 28 days' detention was stretching it but I can just about live with that. But 42 days is beyond the rubicon."

He said: "And we, in Northern Ireland, have bitter experience with internment that this sort of law – which breaches people's human rights and erodes civil liberties – will backfire.

"I regret now that during internment I was not mature or experienced enough to speak out strongly against it. I regret that."

The UUP peer accepted that the emotional public response was to support powers for the police to hold terror suspects for 42 days, or even longer.

And Lord Laird urged people to set aside emotion and think of "personal freedoms" – suggesting that 28 days was "plenty of time to charge someone".

He said: "Gordon Brown knew this legislation would not get through the Lords.

"He is playing politics with it. Beating his chest and playing to the gallery and popular opinion. It's the lowest of the low to play politics with terrorism."

Asked about the different vote the UUP would take in the Lords, compared to Lady Hermon in the Commons, Lord Laird concluded: "Our (the UUP peers') position has been known for about a year. We have been consistent on it and never suggested it would change.

"I will definitely be voting for 28 days' detention (not 42 days) and I have no information to suggest my colleagues will be doing any different."