AV referendum: Union stance 'depressing', says Johnson
Alan Johnson has criticised trade unions planning to campaign against changing the UK voting system.
The former home secretary, who backs a switch to the alternative vote, said electoral change was a "founding principle" of the union movement.
Reports that most union leaders would campaign to keep first-past-the-post were "depressing", he said.
Meanwhile 25 historians have said AV would threaten the principle of equal votes - ahead of the 5 May referendum.
The AV referendum was a key part of the coalition deal between the Conservatives, who want to keep the current system, and the Liberal Democrats, who want to change it.
Voters will decide whether to keep first-past-the-post, where voters put a cross next to their chosen candidate, or switch to AV, where candidates are ranked in order of preference.
The Financial Times reported on Wednesday that at least five trade unions would send out anti-AV leaflets to their members - including the GMB, Aslef and the Prison Officers' Association - and had joined the official No2AV campaign while Unite, the biggest union, was also campaigning against AV.
Mr Johnson told BBC One's This Week programme the low point of his week had been "the rather depressing news that every trade union, apparently, is going to oppose AV in the referendum".
"Given that the trade union movement, their founding principles were electoral reform, given this depressing conservatism on electoral reform, they now have an opportunity in a referendum to actually speak up for change - which they have been arguing for for years - suddenly most unions seem to be going against it."
He said only Billy Hayes - general secretary of the Communication Workers' Union, which Mr Johnson himself used to be head of - had come out in support of AV.
However, the PCS union, which represents 300,000 staff in the civil service and government agencies, later made clear that it advised its members last month to support AV.
Mr Johnson said he thought most union members would "vote the way they think they should vote, rather than the way they are told to vote".
GMB General Secretary Paul Kenny said his union had "long held the policy that the tried and tested first-past-the-post is the system that should be used for general elections for the UK Parliament".
He said first-past-the-post delivered strong, single-party government, was easy to understand and had a "strong constituency link".
"Alan Johnson and Nick Clegg are asking to people to vote for an electoral system that is not anywhere in the world apart from Fiji, Papua New Guinea and Australia. "Even those who want proportional representation agree with Nick Clegg that AV is 'a miserable little compromise'," he said.
A spokesman for the No2AV campaign said: "The vast majority of the major unions are lining up against AV."
Mr Johnson and Labour leader Ed Miliband are among Labour MPs backing a change to AV - but many heavyweight figures within the party, including former Deputy Prime Minister John Prescott, and most Conservatives, are campaigning to keep the current first-past-the-post system for Westminster elections.
In a letter to The Times, signed by Niall Ferguson and Anthony Beevor among others, 25 historians argue that first-past-the-post is the product of a long fight for one vote for every man or woman.
They claim this principle of "equal votes" would be threatened by a move to AV - where second preference votes given to the candidate with the least support are re-distributed after the initial ballot if no-one gains over 50% of first preference votes.
The letter was organised by the historian turned Conservative MP Chris Skidmore, not the official No to AV campaign.
"The cause of reform, so long fought for, cannot afford to have the fundamentally fair and historic principle of majority voting cast aside," the historians write.
"Nor should we sacrifice the principle which generations of men and women have sought: that each being equal, every member of our society should cast an equal vote."
However 11 leading businessmen have endorsed AV in a rival letter to the Daily Telegraph - in a move which was independent of the official Yes campaign.
The signatories, who include Aviva chairman Lord Sharman, Home Retail Group boss Terry Duddy and top corporate PR executive Roland Rudd, said they were speaking in a private capacity.
AV would make MPs "work harder" to get elected, they claimed, as they would need to aim to secure a majority of voters' support in their constituency.
The current system forced parties to "sacrifice stability for short-term electoral gain", they added and AV elections would give "greater legitimacy" to political parties.
"A vote for change on 5 May would be a victory for fairness, a break with a system of the past and a foundation for greater political stability. It would be good for the country and good for business."
The Liberal Democrats have long campaigned for a more proportional voting system, with the single transferable vote their favoured option, but the Conservatives agreed to a referendum on AV as part of the coalition deal.
No to AV launched a new part of its campaign on Friday, aimed at supporters of proportional representation.
The "No to AV, Yes to PR", is backed by former SDP leader Lord Owen. It aims to attract people "disaffected by the decision of the long-standing supporters of proportional representation - like the Liberal Democrats... to back the Yes to AV campaign".
Lord Owen said he was supporting a "no" vote in the referendum because AV "can produce wildly disproportionate results, and the second preferences of the least favoured candidate carry the least weight".
Voters will cast their ballots on whether to change the voting system on 5 May, in the first UK-wide referendum since 1975.