The secret first draft of the notorious Iraq dossier that helped to take Britain to war is expected to be released tomorrow, in a victory for freedom of information campaigners.

The early version written by John Williams, then director of communications at the Foreign Office, has been the subject of a three-year legal wrangle amid hopes that it could reveal whether the supposedly intelligence-led dossier was actually based on a press officer's script - and whether it was subsequently 'sexed up' by Alastair Campbell.

The draft is understood not to contain the infamous claim that Saddam Hussein could launch a strike with 'weapons of mass destruction' within 45 minutes, a claim that was central to the final 'dodgy dossier'.

Yesterday Williams attacked the decision to withhold the document for so long. 'If the government withholds a piece of paper, it immediately makes it significant; it almost doesn't matter what it says,' he argued. 'That's what I said at the time: why are we withholding it?'

A former journalist, who left Whitehall in May, Williams said the row was particularly frustrating as he had never wanted the government to produce a dossier. He had argued, he said, that rather than attempting to prove that Saddam did have weapons of mass destruction, the government should have challenged him to prove he did not: 'I was against the idea of a dossier because I thought it was wrong.'

The Hutton inquiry into the road to war on Iraq identified the existence of an early draft by Williams, but was told by Campbell that it had become 'redundant' when John Scarlett, then chairman of the Joint Intelligence Committee linking Downing Street to the security services, took charge of the process. However, an information tribunal last month ruled that the Williams draft should be disclosed. Anti-war campaigners regard it as key evidence of who introduced the most contentious material into the final draft, and whether Scarlett was too heavily influenced by aides with an interest in making a case for war.

Williams said that critics of the war were likely to find significant similarities between his draft and Scarlett's version, but insisted that should not be surprising since both were working with 'the same assumptions, the same policy, with much of the same material'.

David Miliband, the Foreign Secretary, is expected to confirm in a statement to the Commons tomorrow that the government will bow to the information tribunal's ruling, rather than exercising ministerial powers to veto it or challenge it in court. Ministers had argued that the draft should not be disclosed because it jeopardised the confidentiality - and therefore candour - of advice given to them by civil servants.

The release is in response to pressure by Chris Ames, a former charity worker from Surrey, who began pursuing the document early in 2005.

The government will hope that the publication finally draws a line under the sorry saga of the dossier, which led indirectly to the suicide of scientist David Kelly after he was identified as the apparent source of BBC reports that the dossier had been 'overspun' by Campbell.