The controversial claim that Iraq bought uranium from Africa was stated as fact in an early draft of the Government's dossier, new documents before the Hutton inquiry show.
The allegation was watered down in the final version of the dossier to read that Saddam Hussein had merely "sought" material from Niger to develop his nuclear weapons programme.
The revelation that the claim was originally much stronger will fuel suspicions that Britain was forced to amend its dossier after warnings from the CIA that the Niger link was unproven.
It also suggests that the UK was so anxious to portray Saddam as a nuclear threat that it decided to keep even a weakened version of the allegation in its dossier.
The September 10/11 draft of the dossier sets out "what we now know" of Saddam's weapons of mass destruction programmes. "Iraq continues to work on developing nuclear weapons ... Uranium to be used in the production of fissile material has been purchased from Africa," it states.
The executive summary of the dossier also states that "recent intelligence ... indicates" that Iraq "has purchased large quantities of uranium ore, despite having no civil nuclear programme that would require it".
In the final dossier published on 24 September, the claim was much weaker. It stated merely that "There is intelligence that Iraq has sought the supply of significant quantities of uranium from Africa."
It appears that the change resulted from a warning from the CIA, which had concluded that claims that Iraq had bought uranium oxide ("yellowcake") were based on crude forgeries.
John Scarlett, the chairman of the Joint Intelligence Committee responsible for the dossier, may be asked when he gives evidence to the Hutton inquiry today exactly why the earlier draft was so categoric about the Niger link.
The Niger issue caused political damage to President Bush when it emerged that he had repeated the claim in his State of the Union address despite CIA misgivings.
Jack Straw, the Foreign Secretary, admitted in a letter to the Foreign Affairs Select Committee in June that the Americans had warned the UK away from the claim in the dossier. The CIA received its own copy of the dossier on 11 September, and Mr Straw told MPs: "Just before the dossier was finalised, the CIA offered a comment noting that they did not regard the reference to the supply of uranium from Africa as credible."
But the Foreign Secretary insisted that there had been no need to include a "health warning" on the claim because the Government was confident in the "underlying" intelligence.
Britain has insisted it received separate intelligence from a third country, which it could not share with the Americans. "The reference in the dossier was based on intelligence from more than one source," Mr Straw said.
The CIA sent Joe Wilson, a former diplomat, to Niger to investigate the allegations in 2002, and he concluded that they were false. The International Atomic Energy Agency also said earlier this year that documents relating to the allegation were forged.Reuse content