The Conservatives are funnelling hundreds of thousands of pounds’ worth of donations to the party through a secretive dining club that allows donors to keep their identity hidden.

New figures, released today, reveal that in the last four months alone the Tories have been given £140,000 by an organisation called the United and Cecil Club to fund election campaigns in their most marginal seats.

The money was given by donors at lunches and dinners attended by senior Conservative figures, including at least five cabinet ministers, and threatens to embroil the party in an embarrassing new row over cash for access.

Download the new Independent Premium app Sharing the full story, not just the headlines

Campaigners for transparency in party funding called the disclosure “astonishing”, expressing dismay that the Tories are using a loophole in Britain’s electoral laws to keep the names of the donors anonymous.

Under Electoral Commission rules, individuals and organisations donating more than £1,500 a year should be named but those giving through a private members’ club are not identified on the register.

The secret donations to the United and Cecil Club make it the Tories’ seventh-largest donor, with their biggest financial support coming from the billionaire hedge fund manager Sir Michael Hintze.

The figures from the Electoral Commission show he gave the Conservatives their single-biggest donation for six years with a £1.5m gift, helping them to lead the funding arms race in the run-up to the next election – raking in £6.6m in first quarter of this year.

The Liberal Democrats got £1,074,482 and Ukip received £493,412, although this did not include any donation from the businessman Paul Sykes who paid for Ukip’s recent high-profile poster campaign. Ukip declined to explain the absence of Mr Sykes.

But transparency campaigners voiced particular concern about the way in which the Conservatives were using members’ associations to mask the identity of some of their donors.

Figures from the Electoral Commission show that over the last year nearly almost £300,000 has been funnelled to Conservative marginal seats from the United and Cecil Club, and as much as £800,000 over the last decade. The club, which is based out of a suburban house in Buckinghamshire, appears to have no website, no contact details and no publicly available membership list.

Inside Politics newsletter The latest news on Brexit, politics and beyond direct to your inbox Enter your email address Continue Continue Please enter an email address Email address is invalid Fill out this field Email address is invalid Email already exists. Log in to update your newsletter preferences Register with your social account or click here to log in I would like to receive updates on politics every morning by email Update newsletter preferences

Yet over the last four months it has funded grants of between £2,500 and £5,000 to 45 Conservative associations – in the most marginal seat which will be vital to securing a Conservative victory at the next election.

Under election rules all donors giving over £1,500 to a political party have to be publicly named. But donors to organisations like United and Cecil – which are member associations – only have to be declared if they give over £7,500.

This gives significant latitude for donors to remain anonymous. Transparency campaigners said this was of particular concern when organisations like United and Cecil provided access for their members to key ministers.

In the past year the Justice Secretary Chris Grayling, the Work and Pensions Secretary Iain Duncan Smith and the Tories’ election strategist Lynton Crosby have all addressed United and Cecil dinners which have been held at the Carlton Club in London.

The Carton Club – which gave David Cameron honorary membership – has also in the past given money to the Conservative Party.

Tamasin Cave, from the Alliance for Lobbying Transparency, said the system was open to abuse.

“It is astonishing in today’s world to find the conservatives deliberately exploiting a loophole that allows its donors absolute anonymity,” she said.

“This is not petty cash either, but sums large enough to help shift voting. If these donors want to influence British politics, they should have the courage of their convictions and declare it.

“This government aspires to be the most transparent in the world. They should start by following the spirit of the rules on donations. Come clean on who your backers are David Cameron. This is not how modern politics is done.”

A Labour Party Spokesman said: “The Tories are increasingly reliant on shadowy supper clubs pumping thousands of pounds in to their coffers, away from the full glare of public scrutiny.

“People will rightly ask why David Cameron – who once said that sunlight was the best disinfectant – feels he needs to use these methods to raise money.”

But a Conservative Party spokesman insisted all donations were entirely proper and accounted for.

“Any donation to United and Cecil over £7,500 is registered in the proper way in compliance with Electoral Commission rules as are all donations to the Conservative Party.”