The 2002 dossier became the centre of controversy after the Iraq invasion
Documents showing intelligence chiefs were urged to make a key dossier on the Iraqi threat as "firm" as possible have led to new calls for a war inquiry.
Intelligence head Sir John Scarlett was pressed in an e-mail to make analysis of Iraq's weapons of mass destruction as "authoritative" as he could.
Details of this e-mail were released under a freedom of information request.
The Conservatives said the evidence was "damaging", while the Lib Dems said it showed the UK was "duped" into the war.
Critics of the war say the dossier, published in late 2002 as US pressure on Iraq was growing, was "sexed up" to press the case for military action against Saddam Hussein.
The Cabinet Office said the documents had been made available to the Hutton and Butler inquiries which examined the government's use of intelligence in the run-up to the war.
"Lord Butler and Lord Hutton confirmed that all intelligence judgements were made solely by the Joint Intelligence Committee with no political interference," a spokesman said.
Other documents released on Thursday appear to highlight concerns within British intelligence agencies about the dossier and its claims about the advanced state of Iraq's weapons of mass destruction (WMD) capability.
The dossier, published in September 2002, contained the controversial claim that Iraq could use biological and chemical weapons within 45 minutes of being ordered to do so.
As head of the Joint Intelligence Committee, Sir John Scarlett - now head of M16 - was responsible for putting together the document - which the then prime minister Tony Blair used as part of his case for action against Iraq.
In an e-mail to Mr Scarlett on 11 September, Desmond Bowen - the then head of the Cabinet Office's defence secretariat - referred to a draft version of the dossier.
The e-mail was also sent to Alastair Campbell, No 10's Head of Communications, No 10 Chief of Staff Jonathan Powell and the prime minister's chief foreign policy adviser David Manning.
"In looking at the WMD sections, you clearly want to be as firm and authoritative as you can be," Mr Bowen wrote.
"You will need to judge the extent to which you need to hedge your judgements with, for example, 'it is almost certain' and similar caveats.
"I appreciate that this can increase the authenticity of the document in terms of it being a proper assessment but that needs to be weighed against the use that will be made by the opponents of action who will add up the number of judgements on which we do not have absolute clarity."
The dossier became the cause of a huge row between the BBC and Tony Blair's government following the invasion of Iraq and the failure to find WMD.
The Today programme's Andrew Gilligan reported that an unnamed senior official involved in drawing it up had told him parts of it - specifically a claim that Saddam could launch WMD at 45 minutes' notice - had been inserted against the wishes of the intelligence services even though the government "probably knew" the claim was wrong.
This led on to the Hutton inquiry into the death of Dr David Kelly, the WMD specialist who killed himself just over a week after being named by the Ministry of Defence as the source for the BBC's report.
Lord Hutton's inquiry ruled that Mr Gilligan's report had been wrong because Joint Intelligence Committee chairman John Scarlett had had ownership of the dossier and had agreed to everything included in it.
Lord Hutton also said the 45-minute claim - which was withdrawn 10 months later - was based on a report received by the intelligence services that they believed at the time to be reliable.
Critics say too many caveats about Iraq's WMD capability were taken out of the final dossier to make the case for action against Saddam Hussein more convincing to the public.
"These minutes shed interesting light on the process by which the caveats in the Joint Intelligence Committee's original assessment of Iraq's WMD programme were stripped out of the dossier presented to Parliament and the British public," said shadow foreign secretary William Hague.
Reiterating his call for a full-scale inquiry into the origins of UK involvement in the invasion of Iraq, Mr Hague said there had a "steady stream of damaging revelations about the events leading up to the war".
For the Lib Dems, foreign affairs spokesman Edward Davey said the documents "confirm the widely held suspicions that leading officials and political advisers close to Tony Blair were deliberately tweaking the presentation of the intelligence to bolster the case for war on Iraq".
The government has always maintained Iraq was a serious threat and it believed at the time that it had WMD capability.
Other e-mails released on Thursday showed that certain intelligence officials complained of "iffy drafting" in the dossier.
In one e-mail, an unnamed official says: "I note that the paper suggests that Saddam's biotech efforts have gone much further than we ever feared."
The official then refers to the claim that Iraq had "assembled specialists to work on its nuclear programme" and added: "Dr Frankenstein, I presume?"
The Cabinet Office said it could not disclose which agencies the officials cited worked for but said they were in "sensitive posts".
The documents were released after Information Commissioner Richard Thomas backed an FOI request to publish them.