MI6 made secret plan for anti-Saddam coup in December 2001

MI6 drew up proposals to support a coup against Saddam Hussein three months after the terrorist attacks on 11 September in the United States, previously classified documents indicate.

The papers outline a proposal for regime change in Iraq backed up by airstrikes. The files were read by the then Foreign Secretary Jack Straw, who described them as "very perceptive". He recommended Tony Blair, who was then Prime Minister, also read the files.

The three documents were written by a senior MI6 officer only referred to as "SIS4" in December 2001.

They were declassified and released yesterday by the Chilcot inquiry. Among the revelations are the following:

* Oil was a key motivating factor behind the efforts to remove Saddam. "The removal of Saddam remains a prize because it could give new security to oil supplies," the officer writes.

* MI6 did not believe that Saddam or Iraq were supporting al-Qa'ida. "There is no convincing intelligence (or common-sense) case that Iraq supports Sunni extremism," it says. But in January 2004, Mr Blair told the Commons: "We do know of links between al-Qa'ida and Iraq. We cannot be sure of the exact extent of those links."

* Britain believed America was planning military action to remove Saddam long before it was officially acknowledged. One document is dedicated to outlining the case for preventing America from taking direct action. They also refer to "US impatience".

But it was the plan to support a coup in Iraq which is most intriguing. The officer wrote: "At our meeting on 30 November [2001], we discussed how we could combine an objective of regime change in Baghdad with the need to protect important regional interests which would be at grave risk if a bombing campaign against Iraq were launched in the short term."

Under the heading a "new route map" the officer goes on to suggest that the West should adopt "an onion" approach to the problem – admitting only part of the plan in pubic but with detailed support for a coup in private.

"The key idea is that it is possible to speak openly about support for regime change in Iraq, without compromising the actual project to support a coup," the documents say. "The overall plan would need to be like an onion – each layer concealing the one below. The whole is a policy statement: 'we want regime change in Baghdad and we are ready to provide air support to coup makers'. The inmost part is knowledge of the coup makers with whom we are in touch and their operational plan. The layers in between would need to include operational plans."

Air support is defined as the act of using aircraft to attack an enemy to assist ground forces. The operational plans suggest a 12- to 18-month timeframe for the plot to work "to meet US impatience". It also questions the legality of Britain supporting a coup. "Government law officers to provide assurances of legality (there has been a serious problem here)," it says.

Mr Straw was asked about the documents when he was recalled by the committee in February. Because of their classification he had been given access to them in advance – in contravention of the inquiry's undertakings.

Yesterday it apologised and released his detailed comments about them. He said his comments that the papers were "perceptive" could in no way be taken as a "commendation of regime change".

He cited the MI6 officer's emphasis on the legality of any coup as the reason why he felt no need to question it.