This month, openDemocracy revealed that the Conservatives had become increasingly dependent on money from Russia-linked donors. Since the start of November, Chernukhin has donated £200,000 to the party, taking her gifts to the Conservatives this year to over half a million pounds.

Other regular guests at Leader’s Group meetings including Rosemary Said, who has given almost £200,000 to the Tories in 2019. Ms Said's husband, Syrian-born Wafic Said, helped broker the UK’s biggest arms sale – the Al-Yamamah deal – signed by Prime Minister Margaret Thatcher in 1985.

A number of senior Conservative donors have received honours including knighthoods and peerages. In September, Tory treasurer Ehud Sheleg received a knighthood, as did outgoing Tory treasurer Mick Davis. Sheleg, an art dealer, has given the party more than £3 million.

One of the Conservatives’ most generous donors, taxi millionaire John Griffin, has criticised the party’s reliance on wealthy benefactors, and urged a “more energetic” approach to soliciting small donations from ordinary members. But there is no sign of any change in direction.

Off-the-record soirées with the Tory top table

The Leader’s Group meets at least once each quarter. Soirées have been held at the homes or corporate dining suites of big donors and key party figures. No records are kept of any discussions that take place at these events, but they frequently attract the top table of the Conservative Party.

As well as Theresa May, David Cameron and George Osborne, frequent attendees at Leader’s Group events have included important figures in the recent Conservative administrations. Michael Gove, Ian Duncan Smith and Sajid Javid were all present at numerous Leader’s Group meetings between 2013 and 2018.

One Leader’s Group donor, Neil Record, chairman of the think tank the Institute of Economic Affairs, previously said of the group: "The donors are treated like an intelligent fan club. If there is a businessman who wants to have a chat with a future prime minister then this is his opportunity."

The previous Labour government was dogged by donations controversies. In 2006, Labour peer Lord Levy was arrested but not charged during the ‘cash for honours’ scandal, in which businessmen who gave loans to the party were subsequently recommended for peerages. Levy denied wrongdoing.

Hedge funds and pheasant shoots

In early February 2018, leading Conservative lights gathered among the dinosaurs at the Natural History Museum in London for the party’s Black and White fundraising ball. Guests dined on slow-cooked beef and drank expensive wine.

The highlight of the night was the auction. As well as dinner with Michael Gove and Sarah Vine for £120,000, guests could also bid for a 500-bird pheasant and partridge shoot at Maristow & Bickleigh estate near Plymouth, sponsored by Andrew Law and his wife.

Law, who is one of the hedge fund industry’s most successful money managers, has given almost £3 million to the Conservatives since 2010, and attended at least fourteen Leader’s Group meetings. He is one of a number of successful hedge fund managers among the Tories’ biggest donors.

More than 40 per cent of the Leader’s Group donors owe their wealth to investment firms – a combination of finance, hedge funds, private banking and private equity.

Collectively these donors have given more than £50 million to the Conservatives since 2010. Firms that describe themselves as hedge funds are particularly influential - just five wealthy donors who have been involved with hedge funds have donated more than £18m over the last decade.

Lord Michael Farmer, co-founder of hedge fund Red Kite and one of the most regular attendees at Leader’s Group meetings, has donated over £6.4 million. His son, George, is also a member of the elite group of Tory donors. George Farmer has also donated to the Brexit Party and headed up the British wing of the controversial right-wing US student group Turning Point.

Former Tory party co-treasurer Stanley Fink – nicknamed the ‘godfather’ of the UK hedge fund industry – has given the party more than £1.75 million.

Another Tory donor is Michael Hintze, one of Britain’s wealthiest hedge fund managers, who is worth about £1.4 billion. He has donated £4.1 million to the Tories since 2002. Hintze, a major donor of the Vote Leave campaign, is one of the few known funders of the climate change-denying Global Warming Policy Foundation.

The Conservatives’ growing dependence on hedge fund donors has not gone unnoticed. In September, former chancellor Philip Hammond declared that Boris Johnson was in league with financiers who, he said, stood to profit handsomely from a no-deal Brexit. The prime minister’s sister, Rachel Johnson, agreed.

Economist Frances Coppola says that the Conservatives’ reliance on hedge fund donors is not an orchestrated attempt to make money from Brexit but shows that the interests of a very small subset of the financial industry now have a hugely disproportionate influence on the Conservative Party.

“The Tory party is now wholly unrepresentative in any way of the UK population – its source of funds is so restricted,” said Coppola. “And because they are so dependent on this small group of donors, Tory party policy is going to be skewed.”

“These are all people who want to see a bonfire of regulation, a Singapore-on-Thames,” added Coppolla. “They want to dismantle all state regulation, lower taxes to zero.”

Such views are not a secret. Months before the referendum, over a hundred City executives including former Conservative treasurer Peter Cruddas signed an open letter that called for a slashing of red tape and divergence from EU standards after a Brexit vote.

Another Tory donor group, the Chancellor's Group, for those who give £25,000 a year, was formerly chaired by Dominic Johnson, a donor and party treasurer who founded the Somerset Capital investment firm in 2007 with Jacob Rees-Mogg.

Big oil and ‘unsavoury’ regimes

Energy companies are also heavily represented among Tory Leader’s Group donors. All but one firm is involved in fossil fuels.

Ian Taylor, boss of the world’s largest oil trader Vitol, has given almost £2.5 million. As the Financial Times noted in a 2018 profile, Taylor “has done business with some of the least savoury regimes in the world, from Castro’s Cuba to Saddam’s Iraq, via Africa, the Balkans and Central Asia”.

Ayman Asfari, chief executive of UK oil and gas firm Petrofac, has given the Tories nearly nearly three-quarters of a million pounds. Both David Cameron and Theresa May were criticised previously for lobbying the Bahraini government on Petrofac’s behalf.

Asfari was questioned by the Serious Fraud Office over allegations of bribery and corruption at the Jersey-based company. Earlier this year it emerged that the British government had underwritten a £750 million loan to Petrofac following meetings between Asfari and two cabinet ministers in 2016. The company said the meetings were in a personal capacity and related to the humanitarian crisis in Syra.

There is no evidence that the hedge fund bosses, property magnates, oil executives and others involved have ever tried to, or succeeded in influencing government policy. But critics warn that the secrecy surrounding the Leader’s Group events will inevitably raise suspicions.

Public concern

Labour shadow cabinet minister Jon Trickett has written to Tory chairman James Cleverly calling on the party to publish all the details of the Leader’s Group.

“Your party has failed to honour previous promises to publish details of the Leader’s Group dinners on a quarterly basis. The last Leader’s Group update on your website is from the second quarter of 2018 – 18 months ago,” Trickett wrote.

“Your party’s secrecy on this matter adds to what is a deeply disturbing set of affairs and highlights the need for much greater transparency in how the Conservative Party handles its political donations and relationships with rich and powerful elites.”

Liberal Democrat Tom Brake said: “‘Nothing to hide, nothing to fear’ has long been an ill-judged Conservative mantra, so you can only really draw one conclusion from the fact that they’ve stopped declaring attendees at donors’ dinners, despite David Cameron’s promise to come clean.

“Complete transparency is critically important for a functioning democracy, and it’s vital that all parties uphold this.”

Sarah Clarke from campaign group Unlock Democracy called the Leader’s Group "just the latest example of the UK’s pay-to-play politics, which enables the super rich to buy power and influence.

“While money is pumped through the veins of our political system, our collective future will be determined by the highest bidder. That is not democracy, that is plutocracy.”

A Conservative Party spokesperson said: "The Conservative Party is funded by membership, fundraising and donations, including over 600 local associations across the country and it is this small-scale, grassroots support which is the bedrock of the Party. The Electoral Commission figures exclude the significant sums we have received from small donations.

“All reportable donations are properly and transparently declared to the Electoral Commission, published by them, and comply fully with the law.”

Additional research by Adam Ramsay

Correction, 26 November 2019: Dominic Johnson is no longer the chair of the Chancellor's Group.