The Information Tribunal's decision to order the Foreign Office to release a secret early draft of the dossier on Saddam Hussein's "weapons of mass destruction" is offering new insights into how the government spun the case for war.

In particular, it has become clear that the false claim that Iraq had "purchased" uranium originated in this secret draft, written by the FO press adviser John Williams. While we wait for the FO to publish the document, MPs have called on the government to come clean about the uranium claim and the precise role the Williams draft played in making the case for war.

The existence of the Williams draft, suggesting that a spin doctor had a large hand in writing the WMD dossier, was revealed in the New Statesman in 2006. Making the order that it should be published, the Information Tribunal revealed that there are similarities between that draft and later versions. During last month's hearing it emerged that these included a claim about uranium that was unsupported by intelligence.

The draft dossier that immediately followed Williams's version, drawn up by John Scarlett, then head of the Joint Intelligence Committee, claimed that Iraq had actually purchased uranium. By the time of the final WMD dossier, published in September 2002, this had been watered down to say that Iraq had "sought" uranium from Africa, and was cited as evidence that Iraq was developing nuclear weapons.

It is now known that the CIA doubted both versions. The British government has always claimed it has "credible" and "separate" evidence for the dossier's allegation. But it is now clear that the CIA knew about the separate intelligence and doubted that too.

The "uranium from Africa" claim became highly controversial after President George W Bush quoted it in his January 2003 State of the Union speech, shortly before the start of the Iraq War. Weeks later, the International Atomic Energy Agency (IAEA) announced that documents it had received, "which formed the basis for the reports of recent transactions", were actually crude forgeries.

The controversy deepened in July 2003 when the former US diplomat Joseph Wilson let it be known that he had visited Niger and discounted the possibility that Iraq had sought uranium. In retaliation, the Bush administration leaked the fact that Wilson's wife, Valerie Plame, was a covert CIA agent. Following a criminal investigation, Scooter Libby, chief of staff to Vice-President Dick Cheney, was given a prison sentence for perjury and obstruction of justice, which Bush commuted.

The US withdrew the uranium claim after Wilson's reve lation, but Tony Blair insisted that Britain had separate intelligence. Lord Butler's review of pre-war intelligence described the dossier's uranium claim as "well-founded", based on intelligence it had seen. In fact, the New Statesman can now report that the intelligence was from Italy - the source also for the US intelligence that led to Wilson's Africa trip.

Since the uranium controversy, the government has insisted that it had both a source separate from the fake documents and intelligence it could not share with the US because it came from another country. But it is now clear that Britain has no remaining credible source that was unknown to the US.

Before Williams worked on the draft, the dossier's section on WMDs merely claimed that uranium had been "sought". Yet Scarlett's "first draft" asserted, for the first time in a published document, that the material had been "purchased". This was shown to the CIA on 11 September 2002.

The Butler review reports that: "The CIA advised caution about any suggestion that Iraq had succeeded in acquiring uranium from Africa, but agreed that there was evidence that it had been sought." George Tenet, the CIA's former director, later said the agency had been sceptical even of a claim about "acquisition attempts": "[The agency] expressed reservations about its inclusion but our colleagues said they were confident in their reports and left it in their document."

Britain learned later that its original intelligence, almost certainly from France, was based on the forgeries. The US did not know about France's intelligence until November 2002.

It appears that Britain acquired the intelligence, which it still stands by, during September 2002, possibly while consulting the US. A source who has seen the material has said that it originated from Italy, which reported a visit by a high-level Iraqi delegation, including two generals, to Niger.

Butler inquiry insiders insist this evidence proves that Iraq sought uranium. However, a source in the US has confirmed that the intelligence that led the CIA to send Wilson to Africa in February 2002 was also from Italy. This intelligence relates to the same visiting delegation. Wilson has maintained that he thought it impossible that Iraq had been seeking uranium.

Further questions

At the time of the dossier, neither the US nor the UK had seen the fake documents, which the US acquired in October 2002. In June 2003, an internal CIA document stated that, with the documents discredited, there was no longer "sufficient other reporting to conclude that Iraq pursued uranium from abroad".

As we wait for the Williams draft to be published, the Foreign Office has refused to deny that this draft makes the same false claim as Scarlett's version. The FO has also declined to say that it has credible intelligence that was unknown to the US. The Tory MP John Baron says: "If the Williams draft contains a claim about uranium which turned up in John Scarlett's draft, it raises further questions about the government's assurances to Lord Hutton and to parliament that the draft was immediately redundant. The government must now publish the Williams draft as the tribunal has ordered."

The Labour MP Lynne Jones has put down parliamentary questions based on the New Statesman's information. She says: "The government has always implied that it had a credible source that was not known to the US when it expressed concern over the uranium claim. If that is not the case, this is an example of the government misleading parliament."