In the document, written in late 2002, John Williams, director of communications at the foreign office, said: "Saddam remains the only man to have used chemical weapons to wage war on civilians: so far.
"It is not speculative to suggest he would do so again if he could: he has done it. And we know that he is now re-equipping himself with chemical weapons, while seeking to extend the range of the missiles that would carry them."
The much-disputed 45-minute threat was made in what came to be known as the "dodgy dossier", a document the BBC subsequently alleged was "sexed up" to make the case for war stronger.
A hunt for who might lie behind the BBC's reporting ensued, and David Kelly, a government weapons expert, later committed suicide, prompting a high-level inquiry into the affair.
Britain had sought to prevent Williams' draft being released because it argued that those who draft policy documents should not fear that their ideas might end up being made public.
However, a freedom of information tribunal eventually ruled against them and last month ordered the draft to be released.
The foreign office published it on its website on Monday.
Because Williams' draft makes no mention of the 45-minute claim, but a later government dossier did, it had been suggested that some degree of "sexing up" must have taken place.
But the government said several people were working on draft documents at the same time and it was another dossier, drawn up by the Joint Intelligence Committee, that ultimately was used to make the case for going to war.
"The document produced by John Williams ... was not commissioned as part of the formal drafting process and was not used as the basis for the dossier the government subsequently published," David Miliband, the foreign secretary, said.
As well as the claims about chemical and biological weapons, which were false as no such weapons were found after the invasion of Iraq, Williams' draft accused Iraq of having government-run "rape squads" to intimidate the population.
"Rape is a standard method of intimidation by the regime," his document said.
"The government personnel card produced here (picture) identifies its holder, Aziz Saleh Ahmed, as a 'fighter in the popular army' whose activity is 'violation of women's honour': in other words, he is a professional rapist."
A parenthetical note adds: "(any more on these people? This is the ghastly single image of oppression we must get into people's minds)."