The papers show that the government's most senior intelligence officer wrote to Alastair Campbell, the prime minister's communications director, to confirm he had withdrawn a conclusion to the report only days before it was made public.

The move casts doubt on government insistence last week that Downing Street did not interfere with the contents of the dossier.

Critics have accused Downing Street of exaggerating claims about Saddam Hussein's weapons to bolster its case for war against Iraq, including a questionable claim that Baghdad could deploy chemical or biological arms in 45 minutes.

MPs last night called on the government to release the original draft of the 50-page intelligence document — including the missing conclusion. "Only if the government agrees to release the undoctored version of the report will we see a full interpretation of the intelligence that was available," said Patrick Mercer, a Conservative member of the defence select committee.

The demands came as Tony Blair claimed yesterday to have new evidence of weapons of mass destruction. Frustrated that questions over Downing Street's role have dogged his travels to the Gulf and eastern Europe, Blair broke off from the celebrations of St Petersburg's 300th anniversary to defend his stance.

In a television broadcast he said he was aware of fresh information based on the questioning of Iraqi scientists. "I certainly do know some of the stuff that has already been accumulated as a result of interviews . . . What we are going to do is assemble that evidence and present it properly to people," he said.

The dossier, published last September, was drawn up by the joint intelligence committee (JIC) — Britain's top intelligence body, made up of the heads of MI5, MI6, GCHQ, defence intelligence and senior civil servants.

Documents shown to The Sunday Times last week make clear the final version was published only after extensive consultation between John Scarlett, the JIC chairman, and Campbell.

The government's security co-ordinator, Sir David Omand, and Sir David Manning, the prime minister's foreign policy adviser, were also involved, along with Blair's chief of staff, Jonathan Powell.

In a memo to Campbell, Scarlett said Blair's "foreword" had been incorporated within the overall document but "the conclusion has been dropped".

Insiders say the memo was the result of a "deal" over the dossier's contents after months of bitter disagreement between intelligence chiefs and Blair's aides.

Campbell had attempted to persuade the intelligence services to incorporate hard-hitting conclusions depicting Saddam as an immediate threat and describing his regime's weapons of mass destruction in simple, unqualified language. The intelligence services were reluctant to agree because, they said, the case against Saddam was not proven.

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