Pauline Neville-Jones, former head of Britain's Joint Intelligence Committee (JIC), which assesses intelligence for the government, said in an interview broadcast on Saturday that
Blair could not escape any similar criticism.
"The buck does stop there (with Blair) and I don't think the political layer in any country can escape the consequences of a systemic failure," she told BBC television.
Former top civil servant Lord Butler will deliver a report next Wednesday on the intelligence the government received about Saddam Hussein's weapons. It is expected to criticise Britain's spymasters and some government figures.
It follows a scathing US Senate committee report on Friday that said American spy agencies overstated the threat of Iraqi weapons of mass destruction, relied on dubious sources and ignored contrary evidence before last year's US-led invasion of Iraq.
But it cleared President George Bush's administration of charges it pressured analysts to reach its own pre-set conclusions.
No weapons programme
Blair persuaded a reluctant parliament and public to back war on Iraq on the basis that Baghdad had biological and chemical weapons and could use them. Yet more than a year after Saddam was ousted, no such weapons have been found.
"The buck does stop there (with Blair) and
I don't think the political layer in any country
can escape the consequences of a systemic failure"
Joint Intelligence Committee, former head
This week Blair admitted for the first time banned weapons may never be found.
Butler's remit was to study the accuracy of intelligence on Iraqi weapons of mass destruction and make recommendations for the future gathering, evaluation and use of intelligence.
Media reports suggest JIC chairman John Scarlett, who has since been named the new head of Britain's MI6 agency, which deals with overseas intelligence, would be singled out for the
Neville-Jones said his appointment by Blair to the MI6 job might now be viewed as "unwise".
"I think having put him in that position, the conclusions of the Butler Committee may bear on whether that is now a sensible thing to do," she said.
Blair will respond to Butler's report with a statement to parliament to try to draw a line under his Iraq troubles, which have caused his popularity and personal trust ratings to tumble.