An unpublished article by weapons expert Dr David Kelly said military force was the only way to ensure full disarmament in Iraq, it has been reported.
Dr David Kelly thought the Iraqis were concealing weapons
The piece was written anonymously just before the war began but only finally printed in this week's Observer, according to the newspaper.
In the report Dr Kelly also said the threat from Iraq was not imminent, and was only "modest".
The revelation came as Foreign Secretary Jack Straw told the BBC weapons of mass destruction may never be found in Iraq.
The new chief UN weapons inspector, Dimitris Perricos, has waded into the row, saying the UK Government's controversial claim some Iraqi chemical and biological weapons could be deployed in 45 minutes was wrong.
On Monday Dr Kelly's widow Janice is due to appear before the Hutton Inquiry hearing into his death at the Royal Courts of Justice.
She will probably give evidence via a video link, to avoid the media scrum which has developed for many other witnesses' appearances.
'Arsenal of weapons'
In his article Dr Kelly argued that there was evidence Saddam still had chemical and biological weapons, and that "key nuclear research and design teams remain in place".
He said "only regime change" could avert the long-term threat of "Iraq's development to military maturity of weapons of mass destruction".
Dr Kelly apparently killed himself after being outed as the source for a BBC story accusing the government of exaggerating intelligence against Iraq in its September dossier.
Andrew Gilligan's report for Radio 4's Today programme sparked outrage in Downing Street and led to demands for a BBC apology and retraction.
The Observer quoted Dr Kelly - a former arms inspector - as writing: "Iraq has spent the past 30 years building up an arsenal of weapons of mass destruction (WMD).
"Although the current threat presented by Iraq militarily is modest, both in terms of conventional and unconventional weapons, it has never given up its intent to develop and stockpile such weapons for both military and terrorist use.
"After 12 unsuccessful years of UN supervision and disarmament, military force regretfully appears to be the only way of finally and conclusively disarming Iraq.
"War may now be inevitable. The proportionality and intensity of the conflict will depend on whether regime change or disarmament is the true objective."
On Sunday Mr Perricos told a Greek newspaper the claim Iraq could inflict overwhelming destruction within 45 minutes "did not correspond to reality" and was "collapsing".
Liberal Democrat foreign affairs spokesman Menzies Campbell said the claim further undermined the government's case for war.
Set up after apparent suicide of Dr David Kelly in July
Dr Kelly was government expert in Iraq weapons programmes
He was named as source of controversial BBC report
Report alleged government had 'sexed up' a dossier on Iraq's weapons capability
Government denies the allegations
He said: "The case for the 45 minute claim is simply withering on the vine.
"We now know that the intelligence was based on hearsay and that any weapons could have only been used on the battlefield.
"This hardly amounted to an imminent threat."
Mr Straw said he could not be certain what would be found in Iraq in the hunt for banned chemical and
biological warfare programmes.
"I can't say precisely what will be discovered. No one can say that," he
told the Breakfast with Frost programme.
But the Foreign Secretary said he still believed military action had been necessary
in the light of Saddam's past record of defiance of the United Nations and the
unanswered questions about his weapons programmes.
"What I can say with absolute certainty is that the decision to go to war
which the House of Commons made by a large majority was justified," he said.