Prof Clements, the director of the National Centre for Peace and Conflict Studies, said the long-awaited Chilcot inquiry report into the war in Iraq was more hard-hitting than expected, but he would have liked it to have gone further.
Prof Clements was secretary-general at the London-based peace organisation International Alert around the time of the 2003 Iraq invasion.
"I thought there would be more culpability associated with Tony Blair's engagement.
"He comes out of it with no glory at all, but I thought it might have said he was more involved in the wilful deception.
"There was absolutely no need for a war ... That was something that we all knew at the time, and that's been vindicated by Chilcot.''
The inquiry, which is to be the subject of an upcoming forum at the peace studies centre, needed to be followed by action, Prof Clements said.
"He could be impeached, even though he is no longer prime minister, for misleading Parliament. That means he [would] no longer [be] able to hold office.
"He was derelict in his duty.''
Prosecution of Mr Blair in the international criminal court was not a realistic option, Prof Clements believed.
While in London, Prof Clements had closely followed the lead-up to the invasion, and he was interested to see how various players, including Mr Blair's Cabinet colleagues, fared in the Chilcot inquiry.
But for Prof Clements, the central figure was Mr Blair.
"He was persuaded, as so many British prime ministers have been, that the only way that Britain can retain its power in the world arena is by joining forces with the United States.
"This is a clear vindication that that is no longer possible ... When anyone blindly follows the US, it is fraught with danger and challenge.''
Reflecting on the hundreds of thousands of Iraqi war deaths, Prof Clements said the inquiry, which took seven years to produce, was "a bit self-indulgent''.
"The Brits are kind of a looking at it as ‘our war, our boys who have lost their lives', but the implications of this are extraordinarily far-reaching.
"They have created chaos and instability in the Middle East, and challenges for the whole world.''
In his opening statement, Sir John Chilcot said Britain joined the invasion without exhausting other options before taking military action.
"The inquiry has not expressed a view on whether military action was legal. That could, of course, only be resolved by a properly constituted and internationally recognised court.
"We have, however, concluded that the circumstances in which it was decided that there was a legal basis for UK military action were far from satisfactory,'' Sir John said.
British newspapers have reported calls for Mr Blair to be impeached under an old law.
● The Chilcot inquiry report has been published online: www.iraqinquiry.org.uk
