A senior Labour figure in Tony Blair's constituency has resigned to support an independent candidate.
Reg Keys' son was killed in Iraq
Derek Cattell is quitting in protest at the Iraq war which he said had raised questions about Mr Blair's integrity.
He will instead support Reg Keys, whose son was killed in Iraq and is standing against Mr Blair in Sedgefield.
Local Labour officials have branded Mr Cattell's move a publicity stunt. The prime minister says he does not regret going to war in Iraq.
Mr Cattell has been on the executive committee of the Sedgefield Labour party for the last 10 years.
He said it was a "big decision" to leave the party he had been a member of for more than 30 years.
But despite wanting a Labour government, he could not vote or work for Mr Blair personally.
"I'm not prepared to vote Labour through gritted teeth," he said.
Mr Keys, 52, is standing on a predominantly anti-war platform.
His son, Lance Corporal Tom Keys, 20, was one of six military police officers killed by an Iraqi mob in Al Majar Al Kabir on June 24 2003.
Mr Cattell said: "Reg is really ramming home the message that Tony Blair's conduct in relation to the whole question of the war raises questions about the prime minister's integrity and honesty."
He urged other candidates to stand aside to give Mr Keys a free run against Mr Blair - something already done by former MI5 officer David Shayler.
Mr Shayler said: "If Reg can beat Blair, then they'll be dancing in the streets of Baghdad and Kabul as well as large parts of Britain."
Mr Blair's election agent, John Burton, hit back at Mr Cattell's comments.
"It is a pity Derek did not contact me before this publicity stunt as I would have told him that I have known Tony for over 22 years and there is no-one that I would trust more," he said.
Mr Burton added: "Derek has always been on the extreme left of the party and has always been against most of what the Labour Government has done.
"Even as a union official he has been opposed to the many things that this government has done for the working people of this region.
"Obviously he is welcome to his views, but I know, and most of the people of Sedgefield know, what this Government has done for us in terms of new hospitals, new schools and new opportunities."
Mr Keys welcomed Mr Cattell's backing, saying: "What better endorsement can I have than from a staunch Labour member for over 30 years?"
Other candidates standing in Sedgefield are: William Brown, UK Independence Party; Robert Browne, Liberal Democrat; Jonathan Cockburn, Blair Must Go Party; Helen John, Independent; Al Lockwood, Conservative; Fiona Luckhurst-Matthews, Veritas; Baroney Maroney Staniforth, Monster Raving Loony Party.