The document, a transcript of a meeting with Tony Blair in April 2004, is already the subject of an unprecedented official secrets prosecution in Britain, against an aide to one of the MPs and another man.

David Keogh, a Cabinet Office employee, is charged with leaking information damaging to international relations to Leo O'Connor, researcher to Tony Clarke, former MP for Northampton South. The two are due to appear in court today for committal hearings.

The document was obtained by Mr Clarke, who in turn consulted his parliamentary colleague, Peter Kilfoyle. The two politicians later decided to pass on part of the contents to a contact in the US.

Mr Kilfoyle, MP for Liverpool Walton and a former defence minister, said last night: "It's very odd we haven't been prosecuted. My colleague Tony Clarke is guilty of discussing it with me and I have discussed it with all and sundry." Asked if he had broken the act, he said: "I don't know. But I'd be very pleased if Her Majesty's finest approached me about it."

Mr Clarke said: "I believe my ex-employee did little wrong."

The two MPs decided in October 2004 to reveal the key information in the transcript to John Latham, a Democrat supporter living in San Diego, California. They hoped to influence the impending 2004 US election, Mr Kilfoyle said.

In San Diego, Mr Latham, 71, a retired electrical engineer and a "contributing member" to the Democrat national committee, told the Guardian: "I was kind of amazed and concerned when I heard about it." The MPs also wanted him to send letters with the information to newspapers in Los Angeles and New York, he added. At a Commons meeting, he had been introduced to Mr Clarke by Mr Kilfoyle. Mr Latham, a British expatriate, and Mr Kilfoyle had attended the same school.

Mr Latham said he had never met Mr Clarke before."He mentioned that the document was a transcript of a meeting in Washington DC between Bush and Blair. There had been a proposal to take military action against al-Jazeera at their headquarters in Qatar. This was defused by Colin Powell, US secretary of state, and Tony Blair, thank goodness."

Mr Latham was appalled. "I thought that President Bush must be in the early stages of paranoia." But it was decided not to write to US newspapers at the time. It is understood Democrats feared Mr Bush's behaviour, if exposed, might win him votes, rather than lose them.

As a result, the facts remained secret for more than a year. Within days of the charges being brought against Mr Keogh and Mr O'Connor, however, information in the memo was published by the Daily Mirror. Lord Goldsmith, the attorney general, threatened other newspapers with the Official Secrets Act if they re-published.

Mr Kilfoyle says Mr Clarke - then still a Labour MP - consulted him after first receiving the transcript. "He told me what was in it. He agonised and was very nervous. He decided the right thing to do was to return it to Downing Street." But police then arrested Mr O'Connor and the two politicians decided they should try to reveal the memo's contents in the US.

The Bush-Blair meeting took place when Whitehall officials, intelligence officers, and British military commanders were expressing outrage at the scale of the US assault on the Iraqi city of Falluja, in which up to 1,000 civilians are feared to have died. Pictures of the attack shown on al-Jazeera had infuriated US generals.

A second, Foreign Office, document leaked in May 2004, exposed the misgivings within the British government. That memo said: "Heavy-handed US military tactics in Falluja and Najaf some weeks ago have fuelled both Sunni and Shi'ite opposition to the coalition, and lost us much public support inside Iraq."