Calls for legal and political action against Tony Blair came almost immediately after Sir John Chilcot unveiled his report into the Iraq War.
Chilcot told the audience at the Queen Elizabeth II conference centre: "We have concluded that the UK chose to join the invasion of Iraq before the peaceful options for disarmament had been exhausted. Military action at that time was not a last resort."
Lindsey German, convener of the Stop the War Coalition, said Chilcot's report underlined everything the group had been saying for more than a decade.
She told the Press Association: "We have been saying for years that Blair was disregarding the UN and was in this hideous relationship with George Bush.
"Chilcot should not be the end of the matter - it must be the beginning of legal and political action against Blair."
Eddie Hancock, from Wigan, whose 19-year-old son Jamie Hancock was a kingsman with the Duke of Lancaster's Regiment when he was killed in Basra in 2006, said Chilcot's report was no whitewash.
He said: "What he has actually said is that Blair undermined the United Nations. Now, if somebody does that, you would think that the act was illegal. He's also misled parliament, he's fabricated facts and misrepresented them.
"I hope ... that for the grievous damage this man has inflicted on this nation, on its armed forces, that he be banned from any form of public office for life. At the very least."
Amnesty International UK director Kate Allen also called for further action.
She said: "Hundreds of thousands of people died in Iraq, during the invasion and its extended aftermath, including UK service personnel. It's therefore vital that lessons are learnt after Sir John Chilcot has so comprehensively pointed towards what some of those are.
"One way of showing that the Government has tried to learn lessons from Iraq would be for it to ensure that all credible allegations of unlawful killing, torture and unauthorised detention at the hands of the UK armed forces in Iraq are properly investigated."
Tony Blair responded to the report in a statement.
He said: "The report should lay to rest allegations of bad faith, lies or deceit. Whether people agree or disagree with my decision to take military action against Saddam Hussein; I took it in good faith and in what I believed to be the best interests of the country."
"However the report does make real and material criticisms of preparation, planning, process and of the relationship with the United States. These are serious criticisms and they require serious answers."
He continued: "I will take full responsibility for any mistakes without exception or excuse."