In a ruling on a freedom of information request relating to what is alleged to be the first draft of the dossier published in 2002, the tribunal said that the public should be allowed to read the document.

The tribunal made its ruling following a three-year campaign by a researcher who believes that the dossier will undermine the government's claims that the document was entirely drawn up by John Scarlett, the then-head of the joint intelligence committee, and not government spin doctors.

The dossier, which claimed Iraq could launch weapons on of mass destruction within 45 minutes, became the subject of huge controversy when the BBC reported that it had been "sexed up" by Downing Street.

Today's decision relates to an early version of the dossier written by John Williams, a former Daily Mirror journalist who at the time was head of press at the Foreign Office. The so-called "Williams draft" was mentioned during the Hutton inquiry but it was never published and at the time the Foreign Office claimed that it had little influence on the version that was eventually published.

The government always claimed that the dossier eventually published in September 2002 was the work of the joint intelligence committee and its chairman, Scarlett.

But Tony Blair was subsequently accused of "sexing up" the dossier to persuade the public to support the war against Iraq and at the time of the Hutton inquiry there was a fierce debate about the extent to which his spin doctors, and principally his press chief, Alastair Campbell, were involved in the wording of the document.

Willliams, who has now retired from the Foreign Office, apparently started writing his version on September 7 2002, four days after Blair had announced that a dossier on Iraq's WMD would be published.

At the time of the Hutton inquiry the government insisted that the dossier drafting process had started later and that the Williams version was not relevant.

It was admitted that Williams had attended meetings to discuss the dossier, but it was claimed that he was not "part of the joint intelligence committee machinery" and that his input was marginal.

After considering evidence from the Foreign Office, and reading the Williams draft itself, the tribunal said that the Williams version should be made public.

"Information has been placed before us, which was not before Lord Hutton, which may lead to questions as to whether the Williams draft in fact played a greater part in influencing the drafting of the dossier than has previously been supposed," said the tribunal, which has the job of adjudicated when public bodies do not accept an order from the information commissioner to release information.

Chris Ames, the researcher who demanded the publication of the Williams draft and whose campaign was supported by the New Statesman, said that today's ruling "casts doubt over the government's claim that the document played no part in the production of the dossier".

In its ruling, the tribunal said that the Williams draft had a "header" at the top with the words "JIC Two Document Version 24 July 2002". The Foreign Office claimed that the reference to JIC - the acronym for joint intelligence committee - was a mistake and that it should have read CIC. CIC was the acronym for the coalition intelligence centre, a Whitehall body set up to coordinate news during the so-called "war on terror".

The tribunal also pointed out that the Williams draft had been annotated in two sets of handwriting. It said that this contradicted the Foreign Office's claim that the Williams draft was discarded as soon as Scarlett started drawing up his own version.

According to the tribunal, "some sections of the published draft do bear a resemblance to parts of the Williams draft". However it said that the similarities "were not such as to lead on easily to the conclusion that one had been based on the other".

During the Hutton inquiry - which covered the drafting of the dossier in detail because the row about Campbell's involvement in it eventually culminated in the death of the weapons expert David Kelly - there were hints that the Williams draft contributed to the final version.

An email from a Downing Street press officer was released in which he referred to "some quick thoughts on John's draft of 9 September".

The email ended: "We also need to think, once we have John's further draft tomorrow, how we prepare the ground for the launch of the text to get expectations in the right place".

Although Williams wrote his draft in September, the Foreign Office had originally started work on a dossier about the WMD threat posed by Iraq and other countries in February 2002. This paper was adapted as the year went on.

When Campbell gave evidence to the Hutton inquiry, he claimed that all previous papers relating to WMD were "redundant". He was anxious to refute suggestions that he and his team of spin doctors had influenced the content of a document that was supposed to reflect the opinions of the intelligence services.

The tribunal said there should be only a "very small redaction in the manuscript annotation" before it is disclosed. The information is "not central to the purpose or content", it added.

A Foreign Office spokesman said: "We will be studying the decision of the tribunal."

John Baron, a Tory MP, said that the Foreign Office ought to comply with the tribunal's ruling.

"I am now pressing the foreign secretary immediately to make public the Williams draft so that we can assess for ourselves the significance of this document in the run-up to war - a war which we should never have been party to."

After today's ruling, Williams told that the BBC that he always felt his draft should have been published and that he thought it was a mistake that the Foreign Office tried to keep it secret.

"I was surprised when the Foreign Office said it was not going to publish this. My feeling has been that by refusing to publish it they have given it the apparent importance which I do not believe it has," he told the BBC.

Williams said that his version was "over-taken" and that it was "never, as far as I was concerned, relevant [to the final published version]."

The BBC story about Downing Street allegedly "sexing up" the dossier claimed that the assertion about Saddam Hussein launching WMD in 45 minutes was added to the dossier at the last minute because Blair and his officials felt early drafts were not very convincing.

Williams told the BBC that his version did not contain the 45 minutes claim.

During the Hutton inquiry, it was established that MI6 only gathered the intelligence about the WMD being launched within 45 minutes - intelligence which turned out to be wrong - shortly before the dossier's publication.