Sir Richard Dearlove, 68, has spent the last year writing a detailed account of events leading up to the war, and had intended to only make his work available to historians after his death.
But now Sir Richard, who provided intelligence about Saddam Hussein's Weapons of Mass Destruction (WMDs) that was apparently 'sexed up' by Tony Blair's government, has revealed that he could go public after the Chilcot Inquiry publishes its findings.
Sir Richard is expected to be criticised by the inquiry's chairman, Sir John Chilcot, over the accuracy of intelligence provided by MI6 agents inside Iraq, which was used in the so-called 'dodgy dossier'.
Now the ex-MI6 boss, who is Master at Pembroke College, Cambridge University, has said: “What I have written (am writing) is a record of events surrounding the invasion of Iraq from my then professional perspective.
“My intention is that this should be a resource available to scholars, but after my decease (may be sooner depending on what Chilcot publishes).
“I have no intention, however, of violating my vows of official secrecy by publishing any memoir.”
Sources close to Sir Richard said that he insists Chilcot should recognise the role played by Tony Blair and the Prime Minister's chief spokesman Alastair Campbell in informing media reports which suggested Saddam could use chemical weapons to target British troops based in Cyprus, a claim which led to Britain entering the war in Iraq.
Sir Richard is said to remain extremely unhappy that this piece of intelligence, which his agents stressed only referred to battlefield munitions which had a much shorter range, led to media reports that UK bases were under threat.
However, he accepts that some of MI6's information on the WMDs was inaccurate, the Mail on Sunday reported.
Mr Blair and Mr Campbell have repeatedly denied making misleading statements about WMD.
Last week it was revealed that Sir John had written to Prime Minister David Cameron informing him of his intention to write personally to those individuals he intends to criticise, with Tony Blair reported to be among those on Sir John's list.
Sir Richard has taken a sabbatical from his duties at Cambridge University to research and write his record of events, and is expected to resume his Master's role at the start of the new academic year.
A security source told The Mail on Sunday: “This is Sir Richard's time-bomb. He wants to set the record straight and defend the integrity of MI6. And Sir Richard has taken a lot of personal criticism over MI6's performance and his supposedly too-cosy relationship with Mr Blair.
“No Chief of MI6 has done anything like this before, but the events in question were unprecedented.
“If Chilcot doesn't put the record straight, Sir Richard will strike back.”
Last night the committee's chairman, Sir Malcolm Rifkind, who was appointed in 2010, offered Sir Richard his support, saying: “I have never heard of a former MI6 chief putting something out there in these terms but I would be interested in what Sir Richard has to say in response to the Chilcot Inquiry which is clearly going to have some meat in it.
“I know Sir Richard and worked with him in the Foreign Office many years ago. He is a very able man of the highest character and a man of his own opinions. We shall have to wait to see what he says.”
Last night, Alastair Campbell and the office for Tony Blair declined to comment on Sir Richard's account.