A high ranking British diplomat, who quit over the war with Iraq, has called policy in the region a "rank disaster".
Mr Ross complained of "politicisation" of diplomatic service
Carne Ross told MPs the intelligence presented to the public about weapons of mass destruction was "manipulated".
He also added that "the proper legal advice from the Foreign office on the legality of the war was ignored".
Mr Blair has always defended the war's legality and the Butler inquiry said there was no evidence of "deliberate distortion" of intelligence on WMD.
During his evidence to the Commons Foreign Affairs Committee Mr Ross also attacked the "politicisation" of the diplomatic service, and claimed promotion depended on agreeing with ministers, most specifically Mr Blair.
Mr Ross, who told MPs he had been a friend of weapons scientist Dr David Kelly and had worked on "early versions" of the government's 2002 dossier on Iraq's WMDs, said he accepted the prime minister was ultimately responsible for foreign policy.
But he added: "Policy making in the run up to the Iraq was, I think, extremely poor in that I don't think the proper available alternatives to war were properly considered.
"I think the presentation of intelligence to the public on weapons of mass destruction was manipulated and I think that the proper legal advice from the Foreign Office on the legality of the war was ignored."
Mr Ross, who was head of strategy for the UN mission in Kosovo, and played a leading role in devising policy on Iraq and Afghanistan, said there was a "political element at work in promotions to the most senior levels of the foreign office".
He said he had also noticed a growing tendency for officials "to tell ministers what they wish to hear in order to advance one's own individual prospects".
He told MPs: "There is a kind of subtle and creeping politicisation of the diplomatic service that in order to get promoted you have to show yourself as being sympathetic in identifying with the views of ministers and, in particular, the prime minister.
"Secondly, and this was the case in the Conservative government before Labour took office, decision-making powers have become increasingly concentrated in Number 10... the Foreign Office has become subsidiary to Number 10."
On Iraq, he said the measure of success in foreign policy should be "minimisation of suffering" and "if that is your measure, our policy has been a rank disaster in the last few years in terms of blood shed".
"By that measure that invasion has been a much greater disaster even than Suez," he added.
Mr Ross quit the Foreign Office after giving evidence to 2004's Butler inquiry into the accuracy of the intelligence about Saddam's weapons of mass destruction.
His Butler testimony concluded that the invasion had been unlawful, he told the MPs in a separate, written submission. It also accused the government of misleading the public over the threat posed by Saddam, and of failing to consider alternatives to military action.
He said he had been advised by a lawyer that revealing the contents of his testimony would leave him in breach of the Official Secrets Act.
He was asked to hand over a copy of the document to the committee clerk by Labour MP Andrew Mackinlay, who assured him it would be covered by Parliamentary privilege.
Mr Ross said he would be "happy" to do so but the clerk later said the document was still in the ex-diplomat's possession.
Mr Mackinlay later told the BBC News website he believed the document should be made public, although it would be up to the committee to vote on the issue.
"There is a world of difference between matters of national security and what might be politically sensitive," he added.
In other evidence to the committee, Mr Ross said the Foreign Office's official view before the build-up to war began was that an invasion would lead to "chaos".
Whenever the issue of "regime change" - the stated policy of the US government at the time - came up in bilateral talks, the leader of the UK delegation "would say, with emphasis, we do not believe regime change is a good idea in Iraq and the reason we do not believe that is that we think Iraq would break up and that would lead to chaos if you do that," said Mr Ross.
He added: "That view of course changed in mid 2002."
Asked if the change was down to "political imperatives," he replied: "There was no basis for changing the view from what was going on inside of Iraq.
"What had changed was what the future of our policy would be towards Iraq."
Mr Ross also attacked what he characterised as an almost total lack of Parliamentary scrutiny of foreign policy and an absence of "moral accountability" for the actions of officials.
He said he now considered pre-war sanctions against Iraq - which he helped devise - to be "fundamentally wrong".
Sanctions had been "ill-engineered, misdirected, targeted at the wrong group of people" and the cause of "immense suffering" but he had never been held to account for them.
The ex-diplomat also criticised the "acute" failure of the foreign affairs "or any other" committee to properly scrutinise the government's Iraq policy.