Cartoon by Leon Kuhn

Jack Straw is expected to be quizzed by Scotland Yard detectives over claims of MI6 complicity in rendition and torture.

Downing Street yesterday said the former foreign secretary should be interviewed following claims a Labour minister gave the green light for a Libyan man to be handed over for torture by the Gaddafi regime.

Senior sources said Tony Blair could also be questioned since only he or Mr Straw – who have both maintained their ignorance of the affair – could have signed off on the deal.

The Metropolitan Police have launched a criminal probe into claims that MI6 tipped off the CIA about the whereabouts of Abdel Hakim Belhadj and his wife in 2004, shortly before Mr Blair signed his deal in the desert with Colonel Gaddafi.

MI6 are so keen to cover up their role in the affair that they want to offer Mr Belhadj – once seen as a terrorist threat and now a leading figure in the Libyan transitional government – a hush money payment of more than £1million.

He and his wife are also suing the government, the security services and former MI6 counter-terrorism chief Sir Mark Allen for damages.

Documents found in Tripoli show Sir Mark sent Gaddafi’s intelligence chief Musa Kusa a congratulatory message after the rendition, saying ‘the least we could do for you and for Libya’.

No 10 was drawn into the controversy yesterday after the BBC revealed that the operation had ministerial approval.

David Cameron’s official spokesman said they would ‘cooperate fully’ with the Metropolitan Police probe.

Asked if the police should find out what ministers knew and when they knew it, the Prime Minister’s official spokesman said: ‘Absolutely. The Government will cooperate fully with that investigation.’

Asked if the police should interview ministers from the Labour government, the No 10 spokesman said: ‘They need to follow the evidence wherever it takes them.’

The 1994 Intelligence Services Act specifies that ‘authorisation of acts outside the British Isles’ can only be signed off as a result of ‘authorisation given by the Secretary of State’.

That means one of Mr Straw’s junior ministers could not have given permission, though security sources said it did not preclude the Prime Minister giving the green light himself.

‘It means Jack Straw or Tony Blair or both of them,’ one source with close knowledge of the security services said.

But both men deny involvement. Last year Mr Blair said: ‘We didn’t support rendition as far as I know.’

Mr Straw said last year: ‘The position of successive foreign secretaries, including me, is that we were opposed to unlawful rendition, torture... and not only did we not agree with it, we were not complicit in it, nor did we turn a blind eye to it.’

Security sources have told the Mail that if the case does come to court, MI6 officers will seek to ‘pass the buck’ to ministers. ‘This has the potential to be hideously embarrassing,’ one said.

Sir Richard Dearlove, the former head of MI6, has already sought to pile pressure on Labour ministers, saying last year: ‘It was a political decision for the Government to co-operate with Libya on Islamist terrorism.’

Whitehall sources claim that successive ministers have been lied to by MI6 chiefs about the extent of complicity.

Former Labour foreign secretary David Miliband told Parliament that the British Indian Ocean island territory of Diego Garcia had been used by rendition flights on two occasions in 2002.

Mr Belhadj is now suing the authorities in Diego Garcia because he was also rendered that way.

Coalition sources say Tory and Lib Dem ministers have also been misled by MI6, who made no mention of Sir Mark’s involvement when they briefed the new government on rendition in 2010.