The former Labour leader Neil Kinnock today launches an outspoken attack on senior colleagues in his party who have campaigned with the Conservatives against reforming Britain's voting system.
Mr Kinnock has told The Independent he "simply cannot understand" how John Reid, Margaret Beckett, John Prescott and David Blunkett can back the Conservatives in support of a system which kept Labour out of power for decades.
He warned that unless Labour voters ignored them in Thursday's referendum it would be far harder for the party to regain power again.
"I simply cannot understand how experienced colleagues can mistake the lessons of the last 60 years: that the Tories have profited massively from divisions in the continual anti-Tory majority," he said. "They must recognise the implacable truth – that first past the post is the Tories' lifeline."
Mr Kinnock is the first senior Labour figure to openly attack those in the party who have sided with the Tories on AV.
His comments are particularly significant because of his closeness to the Labour leader, Ed Miliband. Mr Kinnock, who lost two elections to the Conservatives under first past the post, was one of the only senior Labour figures to back Mr Miliband for the leadership and the two are in close touch.
Others on the pro-AV wing of the party share Mr Kinnock's views but are reluctant to speak out for fear of being accused of splitting the party.
"Reid, Prescott and Blunkett are just dinosaurs looking for one last moment in the limelight," said one former cabinet minister. "But in the process they are doing to irreparable harm to the cause of progressive politics in this country."
Mr Kinnock is known to be particularly incensed that Mr Reid – who used to work in his private office – shared a platform with David Cameron as part of the No campaign. "It's just odd," he said. "Especially when John came out with this 'AV isn't British'.
"AV is the electoral system of choice for most parts of our society. Every trade union, every political party, voluntary organisations, churches, clubs, societies of every description have used AV for decades. That's how British it is."
Mr Kinnock said that even in private Mr Reid and others had not been able to make a convincing argument for their opposition to AV.
"They haven't been able to explain why they're doing it to me – they just give me knowing smiles and say first past the post helps us. Well, first past the post almost permanently put the Tories in power for the last 40 years."
Mr Kinnock added that with the changes to the parliamentary boundaries reducing the number of seats in the House of Commons, it would be an even harder electoral mountain for Labour to climb.
"With the huge gerrymander of the new Parliamentary Boundaries Act, Labour has a vested interest in balancing that by a change to at least AV. Having 600 seats helps the Tories so much, and if that's not mitigated by a fairer voting system, then they are laughing all the way to the returning officer."
He added that if there was a No vote on Thursday, it would be those senior Labour figures who would be to blame.
"All Labour voters should simply ask themselves this: why are the Tories pumping millions of pounds into the no vote campaign?"