Former Liberal leader Jeremy Thorpe has joined the election fray, over the "disastrous" aftermath of the Iraq war.
Former Liberal leader Jeremy Thorpe rarely ventures into mainstream politics
Mr Thorpe, 76, challenged Labour and Tory MPs to vow not to back military action without certain justifications. Lib Dem MPs already did so, he said.
Mr Thorpe withdrew from public life after he was acquitted of plotting to kill a former male model in 1979.
Tony Blair defends his decision to go to war. Michael Howard also backs the war, but accuses Mr Blair of deception.
Mr Thorpe, who suffers from Parkinson's Disease, continues to be active in the Devon constituency he once represented and is president of the North Devon Liberal Association, but has rarely ventured back into mainstream politics.
However, he said his anger over the latest revelations about the decision to join the US-led invasion made him feel he should speak out.
He said: "In agreement, like Tweedledum and Tweedledee, Mr Blair and Mr Howard have jettisoned the argument of the existence of weapons of mass destruction as the justification of going to war with Iraq.
"Both have conceded that even if they had known that the intelligence report was inadequate they would still have taken military action.
"The political outcome has been disastrous.
"Every Labour and Tory candidate should be asked to vote against any use of force unless authorised by a United Nations resolution or where the security of the UK is threatened or where British citizens are at risk on foreign soil.
"The Liberal Democrats subscribe to the... considerations. Labour and Tory candidates should be challenged to do likewise."
Mr Thorpe, who will be in Devon for the closing stages of the campaign, said he believed Labour support was "haemorrhaging" and that the Tories had made "no impact" on voters.
Mr Thorpe led the Liberal Party for nine years from 1967, and came almost to the point of sharing in government.
But his political career was left in ruins by a court case - despite the Old Bailey jury clearing him of hiring a hit man to kill former model Norman Scott to cover up an affair the pair were alleged to have had.
A Liberal Democrat spokesperson said it was Mr Thorpe's own initiative to speak out.
"But obviously Liberal Democrat candidates are campaigning across Britain on the way in which Tony Blair appears to have decided to follow George Bush in invading Iraq without being sure of proper legal authority."