Campaigners against reforming Britain's voting system today refused to publish details of the multi-millionaire donors who are bankrolling them.
At the launch of the No2Av campaign in London its director Matthew Elliott said he wanted to see more "transparency" in politics and not a political system "conducted behind closed doors".
But when pressed on whether No2Av would publish details of who was funding its campaign before the planned referendum in May Mr Elliott refused.
Later the No campaign claimed that the Yes Campaign were also refusing to publish a list of their major donors. However a spokesman for the Yes Campaign said it had so far raised £2 million of which 95 per cent had come from two donors: the Electoral Reform Society and Joseph Rowntree Reform Trust.
In an uncomfortable press conference for Mr Elliott he also came under pressure over claims made by No2Av that a ‘yes’ vote in the May would cost the tax payer £250 million.
The estimate was based on £82m to hold the referendum, £9m for voter education ahead of the plebiscite the cost of electronic vote counting at £90m-£130m and £26m for subsequent voter education.
But critics pointed out that Australia uses the Alternative Vote system without the need for electronic voting machines and there are no plans to introduce them into Britain.
The £82 million cost of the referendum was also disputed. The No2Av campaign based its total on the estimated cost of the 2010 General Election. May’s referendum however is being held at the same time the local elections and is thought unlikely to significantly add to the costs of those.
Meanwhile both campaigns engaged in the battle of celebrity endorsements.
The Yes Campaign unveiled Colin Firth and Helena Bonham Carter, who both won Baftas for their portrayal of the royal couple in The King's Speech, as supporters of the campaign.
They will be joined by the comedian Eddie Izzard, Martin Bell, the former independent MP, and Greg Dyke, former Director-General of the BBC, who are to become vice-chairs.
In retaliation the No Campaign revealed that the Labour peer and fertility doctor Lord Winston was backing them.
However at their launch there was no sign of either Margaret Beckett who is President of the campaign or patrons David Blunkett and Lord Prescott.
It was suggested they had been advised to stay away for fear of associating the campaign with “old Labour dinasuars”.
The No Campaign hope to turn the referendum into a poll on the Liberal Democrats in Government.
Mr Elliott, branded the ballot "Nick Clegg's referendum", and said AV would leave the country at the mercy of "political fixes".
"The British people will be staggered to learn that our politicians are considering squandering £250 million of taxpayers' money on a new voting system at a time when they are being told to tighten their belts," Mr Elliott added.
But the 'Yes' campaign dismissed the figures as "fantasy",
Katie Ghose, chairman of the Yes to Fairer Votes campaign, said: "The No camp’s sums don’t add up. Their make-believe machines don’t exist in Australia and won’t exist in the UK.”
Clashes between the campaigns escalated as the parliamentary battle over the referendum also resumed with the Government seeking to overturn a series of defeats inflicted by the Lords.
Time is running out to get the referendum legislation passed in time to meet a watchdog's deadline for a May 5 ballot amid continued opposition to elements of the Bill.
The Parliamentary Voting System and Constituencies Bill was held up in the House of Lords where Labour peers mounted a protracted rearguard action against the legislation, which also includes measures to redraw constituency boundaries and reduce the number of MPs.
Lib Dem leader and Deputy Prime Minister Mr Clegg pulled out of an official visit to Latin America in an effort to ensure the measure gets through this week before MPs take a half-term break.
The Government is making efforts to ensure as many MPs as possible are available to vote.
A Downing Street source said the moves were part of standard efforts to secure a "robust turnout" in the Commons.
The referendum was a key concession to the Liberal Democrats as part of the negotiations which led to them joining the Conservative-led coalition administration.
Last night the Bill was sent back to the Commons by the upper chamber and ministers are seeking to overturn a series of amendments made by peers - including one which would make the referendum result non-binding if the turnout is less than 40%.
There is widespread expectation that the stand-off between the two houses will continue - leading to a prolonged session of parliamentary "ping-pong" tomorrow.