No to AV campaign's cross-party claim under scrutiny as 42 of 53 named donors revealed to be from Tory sources

The official campaign against AV has been almost exclusively funded by Conservative party donors, among them hedge-fund managers, bankers and big City names, raising new questions about the organisation's claims to be cross-party and politically neutral.

An analysis of the most complete set of accounts of donations reveals the extent of the no campaign's reliance on the City for funding and how the Tory party fundraising machine helped shore up support for No to AV, which has seen it strengthening its lead in the polls in the runup to Thursday's vote.

The link between the no campaign and the Tory party's financiers is causing some unease among Labour opponents to AV. But Margaret Beckett, the former foreign secretary, called it a "necessary evil" to counter the arguments of the better funded yes camp.

Both campaigns provided the Guardian with every donation received in recent weeks, updating their previously declared donations.

Despite the support of more than half of the Labour benches, 42 of the 53 named donors to the No to AV campaign are also Tory donors, having given £18.4m between them over the past decade. Nine are not readily identifiable in official donor records, a 10th is official funding from the electoral commission and just one is a Labour donor, the GMB union.

Among the Tory names are seven Conservative peers including Lord Sainsbury of Preston Candover, who has donated nearly £3m to the Tories in six years. Jonathan Wood, who was the biggest shareholder in Northern Rock when it collapsed and later tried to sue the government over its handling of the bank's nationalisation, and Lord Fink, the Tory co-treasurer who has been described as the "godfather" of the UK hedge-fund industry, have both come to the aid of the campaign in recent weeks, giving another £75,000 between them.

Stockbroking and corporate finance group Shore Capital has given £25,000 while hedge fund Odey Asset Management Group, founded by Crispin Odey in 1991, has donated £20,000. Lord Wolfson, the boss of clothing chain Next, gave £25,000.

John Nash, chairman of the healthcare company Care UK, has donated £25,000. His wife has previously donated more than £230,000 to the Tories including, controversially, sums to the health secretary Andrew Lansley, from whose health reforms the company could profit.

Beckett, who is also a member of the committee on standards in public life, which is reviewing political funding, said: "The people who have the money are people who fund the Conservative party.

"This is the truism in politics. I think it's a pity, I'm sorry about it. Am I excited about it? No.

"I would feel really uncomfortable being in a position where the yes campaign has £2m from the off and we aren't able to have any funding to counter their arguments … It's a necessary evil."

The figures reveal for the first time that the yes campaign has now outspent the anti-AV camp by £3.4m to £2.6m, the majority from the Joseph Rowntree Reform Trust and the Electoral Reform Society (ERS). George Osborne has accused the ERS of having a vested interest in a yes vote. The ERS's commercial subsidiary Electoral Reform Services Ltd (ERSL) is printing the postal ballots for the referendum. The organisation has denied it would profit from a yes vote.

The yes camp received an additional £236,579 from the ERS in the past month along with £50,000 from the venture capitalists C&C Alpha Group and £30,000 from Alan Parker, head of Brunswick PR, who has the distinction of being close to both Gordon Brown and David Cameron.

It has also received £75,000 from Paul Marshall, the hedge fund manager and Liberal Democrat donor.

But the No to AV figures do not include donations it received prior to the referendum bill passing in parliament. The law requires that the official campaigns name all donors who give more than £7,500 but it does not apply to the period before the bill got royal assent, during which No to AV lobbied to become the official no campaign. The yes figures include all sums received since it was set up last summer.

Some Labour supporters of the no campaign called on the organisers to fully disclose all their funding sources. An aide to David Blunkett, the former home secretary, said: "He's not involved in any of the administration of the no campaign. But he thinks both campaigns should disclose all their funding."

Martin Bell, the former MP for Tatton and supporter of the yes campaign, said: "We have a right to know who set them up and who bankrolled them from the start."

Tessa Jowell, who is campaigning for a yes vote, said: "I don't agree with my friend and colleague David Blunkett on keeping first past the post but I do agree with him when he says that both campaigns in this referendum should declare all their donors before Thursday's poll.

"That is precisely what the yes campaign has done. We have declared all

our donors since the campaign was set up last summer. Now the no campaign have admitted they have not declared all their donors since they were set up. What do they have to hide? We already know they are 99% funded by Tory donors. What is it they are hiding?

"Voters deserve to know who is behind the no campaign before we go to the polls on Thursday. There is another clear dividing line in this campaign. Those of us in the Yes campaign who believe in transparency - and those running the no campaign who believe in holding information back from the public."

A spokesman for the No to AV campaign said: "There are people who donate – across the political divide – who prefer not to be named when they do. We have disclosed everyone who has donated from the time of royal assent in accord with our commitment.

"Prior to that ... there was no legal basis or reason to disclose our funding sources. It is a much easier job for the yes campaign because they are received funding from two opaque organisations."

• This article was amended on 3 May. The original piece incorrectly stated that the Joseph Rowntree Foundation had donated money to the yes campaign. In fact, the correct name of the organisation that made the donation was the Joseph Rowntree Reform Trust.