Ministers are preparing to offer a £200m “bribe” to encourage a group of Northern Ireland MPs to back Gordon Brown in the critical Commons vote on plans to detain terror suspects for 42 days without charge.

According to the Democratic Unionist party (DUP), a proposal that the power-sharing government at Stormont instead of the Ministry of Defence in London might receive the proceeds of the sale of disused army bases as an enhanced “peace dividend” has been floated in private talks about the counter-terrorism bill.

The informal offer emerged after Geoff Hoon, Labour’s chief whip, warned Brown that more than 60 rebels from his own party were preparing to vote against the bill, which will be debated by MPs on June 11.

With the Tories and the Liberal Democrats opposing it, Brown could be facing his first defeat in the Commons since becoming prime minister.

Brown and Jacqui Smith, the home secretary, last week signalled concessions to increase parliamentary and judicial oversight of the new detention powers. One insider spoke of “desperate late-night phone calls” to some of the rebels.

“Brown has been tugging at the heartstrings, playing the sympathy vote as the wounded premier,” said the insider.

Labour whips have calculated this could sway up to 20 rebels to back the government, making the voting intentions of the nine DUP MPs, including Peter Robinson, its new leader, crucial. Gregory Campbell, the DUP MP for East Londonderry, said this weekend that the offer of cash for Stormont from the army bases had been “floated” by sources close to the government in talks about the party’s position on the 42 days.

Campbell declined to identify those who had made the offer. “It has been mentioned in the ether, among people who have the ear of decision makers,” he said.

He added that the issue of the bases could become critical if the DUP decided this week that the arguments for or against the 42-day law were not in themselves clear cut. “We were initially opposed to internment in Northern Ireland and there are some who would argue that this is a form of internment.

“At the same time, we are very strongly and trenchantly antiterrorist. We have not decided yet and if we remain undecided on how to vote on 42 days then the issue of military bases could come into play,” he said.

“Are we prepared to negotiate? We haven’t ruled it out.”

The bases include Lisanelly and St Lucia in Omagh, Bally-kelly near Londonderry and St Patrick’s barracks in Ballymena.

Additional reporting: Liam Clarke

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