John Prescott has become the most senior Labour figure to call for the party to fight against the adoption of the Alternative Vote (AV) for Westminster elections.
The former deputy prime minister said Labour should make the May 5 vote on AV - and elections to the Scottish Parliament, Welsh Assembly and English councils on the same day - into a "proper referendum"on the Tory-Liberal Democrat Government.
And he savaged his successor Nick Clegg for throwing his weight behind a voting system which the Lib Dem leader denounced before the general election as a "miserable little compromise" and which was now being used as cover for Tory "gerrymandering".
Mr Clegg on Monday confirmed the date for the referendum on whether to ditch first-past-the-post as part of an electoral reform package which would also see constituency boundaries redrawn and the number of MPs cut from 650 to 600. Legislation will be tabled in Parliament before the summer.
In an email message to supporters, the Lib Dem leader said: "The first-past-the-post system hands power to the lucky few who live in marginal constituencies and sucks it away from the vast majority of us who do not. So over the next 10 months the Liberal Democrats will be fighting hard, with others, for a 'yes' vote in the referendum. I want to sweep away the current system and replace it with the Alternative Vote."
Labour offered a referendum on AV in its manifesto for this year's general election. But Lord Prescott said on Tuesday voting reform was being used as "cover for the biggest gerrymandering of seats that I have ever seen in my 40 years in politics". Labour believes that coalition plans to equalise the size of constituencies - due to go ahead in time for the 2015 election regardless of the referendum result - are intended to cost the party seats in Parliament.
Writing on his blog www.prezza.org.uk, Lord Prescott said: "This is a poisonous package and Labour must fight against every single part of it. So let's make the May elections for the Scottish Parliament, Welsh Assembly and English councils a proper referendum on this ConDem government and a set of savage and brutal policies that no-one would have voted for at the last general election."
Lord Prescott accused Mr Clegg of "selling out" his party and Lib Dem voters by backing Conservative austerity measures and said that the referendum on voting reform was his "payoff".
The referendum is already facing opposition on the Labour and Conservative backbenches, with some MPs challenging the plan to hold it on the same day as Scottish, Welsh and council elections, and others demanding that a minimum of 40% of registered voters - as well as a majority of those turning out to vote - should approve any change.
Meanwhile, David Cameron's spokesman has indicated that the Prime Minister will oppose a move to AV, but is not expecting to take an active role in the referendum campaign.