If anybody still seriously doubted that Tony Blair assured George W Bush, up to a year before the war began, that Britain’s Labour government would support a US invasion of Iraq, then the March 2002 internal memo from Colin Powell published on Sunday should finally lay such doubts to rest.

Although in reality, the former US secretary of state’s memo is mere additional confirmation of what is already broadly known, it is likely to add to the pressure on Sir John Chilcot’s long-delayed Iraq war inquiry to clear up the controversy over Blair’s intentions and undertakings in the run-up to war.

In public, Blair continued to insist throughout 2002 that he had taken no decision on whether to support the invasion that eventually began in March 2003. This public testimony is central to his rejection, before the Chilcot inquiry and elsewhere, of claims that he misled parliament and the British people. But within weeks of the meeting at Bush’s ranch in Crawford, Texas, in April 2002, to which the Powell memo refers, details of what the two leaders had privately agreed were leaking into the public domain.

Leaks from officials working for Dick Cheney, Bush’s vice-president, about what Blair had promised at Crawford reached the ears of the Guardian. The result was a front-page lead story, published on 27 July 2002, reporting that the prime minister had committed to backing a war despite public statements in Britain to the contrary. The story disguised the identity and the positions held by the officials.

The Guardian reported: “Tony Blair has privately told George Bush that Britain will support an American attack on Iraq if Saddam Hussein refuses to accept resumed UN weapons inspections. President Bush’s ‘understanding’, based on conversations with the prime minister, is that he can count on Mr Blair according to well-placed Bush administration officials.

“Although no plan of attack has yet been finalised, Mr Blair has already offered ‘in principle’ to lend full British military and diplomatic backing for an assault … A Washington source familiar with administration thinking said that while it was accurate to say Mr Bush had not yet decided how or when to attack Iraq, the president was considering his options in the belief Mr Blair would go along with the US.”

The officials said part of the Blair-Bush understanding at Crawford, followed up at a subsequent meeting at Camp David, Maryland, in September 2002, was that evidence that Iraq presented an urgent threat through its alleged attempts to obtain weapons of mass destruction would be published in London. This was the genesis of that month’s Downing Street “dodgy dossier”, supposedly summarising intelligence assessments. Prepared by No 10’s communications chief, Alastair Campbell, the dossier laid exaggerated stress on the threat posed to Britain by Saddam’s missiles and alleged WMD. In agreeing to do this, a senior military intelligence officer has told the Chilcot inquiry, Blair in effect became chief propagandist for Bush’s Iraq invasion project in Britain and the US.

The Guardian account in July 2002 makes clear that despite his insistence on giving Saddam a chance to comply with resumed UN resolutions on weapons inspections, Blair did not expect this to happen. When Saddam unexpectedly did comply, and when UN inspections under Hans Blix found no WMD, Blair and Bush disregarded their findings and opposed their continuation. The report also threw light on another central controversy in the run-up to war – the necessity, or otherwise, of a new UN security council resolution. France (and China and Russia) opposed such a resolution and the eloquent French foreign minister, Dominique de Villepin, ran rings around the UK foreign secretary, Jack Straw, in a UN debate on the issue in February 2003.

But Straw’s appearance was effectively a dummy run. The officials told the Guardian that Bush and Blair had already agreed in Crawford the previous April that, knowing they would be likely to face insuperable security council opposition, both would adopt the position that invasion and regime change targeting Saddam were allowable under existing UN resolutions. This is exactly what happened.

