Conservative ministers declined to say who they were dining with on Wednesday night as they arrived at the party's secretive summer party, which last year saw donors worth £11bn rubbing shoulders with Britain's most powerful politicians.
The party refused to release the guest list for the event at the private Hurlingham members' club in Fulham, west London, but the gleaming Rolls-Royces and Jaguars streaming through the gates gave a hint of the wealthy passengers heading inside.
Tory ministers including Michael Gove, Nicky Morgan, Matthew Hancock and David Gauke arrived on foot but would not say which donors they would be hosting on their tables.
Two of the biggest donors, Sir Michael Hintze and James Lupton, who have each given more than £1m, were spotted on their way in.
But most guests entered in cars with shaded windows, with some hiding their faces behind their invitations.
The dress code was "glamorous" but unlike last year, invitees were not instructed to avoid black tie.
David Cameron is facing calls to publish the guest list following revelations by the Guardian and the Bureau of Investigative Journalism that the 2013 event attracted bankers, businesspeople and lobbyists jointly worth over £11bn. His spokesman said there was no need to publish a list as the PM was not on "official business".
"Cameron is trying to buy his way to power," said Jon Ashworth, the shadow Cabinet Office minister. "We will be demanding to know who is whispering in his ear at the Hurlingham club."
Last year, when 449 guests paid up to £1,000 a seat, £1.1m in party donations were registered with the Electoral Commission. At the tables were 73 financiers, 47 retail and property tycoons, 10 oil, gas and mining millionaires and 19 people working in public affairs and PR.
Campaigners for political transparency said the event was "a straight-up case of cash-for-access".
At prime minister's questions on Wednesday, Cameron was challenged by Labour MP Kerry McCarthy to reveal what was discussed between defence secretary Philip Hammond and Lord Clanwilliam, a public affairs executive employed by the government of Bahrain, who shared a table last year.
He refused and instead attacked Labour's reliance on finance from trade unions. "The Labour party just has to get one trade union to write one cheque for £14m," he said.
A Tory spokesman said of the summer party: "All donations to the Conservative party are properly and transparently declared to the Electoral Commission, published by them, and comply fully with Electoral Commission rules."
Darren Hughes, deputy chief executive of the Electoral Reform Society, said the revelations were "the latest demonstration of why we need a new, more transparent system for funding political parties".
He added: "Every time we get an insight into how parties raise money, it further cements the impression that our democracy is for sale. Earlier this year we found that three-quarters of the public believe big money has too much influence on political parties, and 61% believe the party funding system is corrupt. Revelations like this are only going to push those numbers in one direction."
Alexandra Runswick, director of Unlock Democracy, an all-party campaign for constitutional reform, said: "The public feels our politics is for sale and that politicians listen to donors and lobbyists but not voters. The big problem is this isn't shocking any more. Voters have started to see this as part of the political process and it shouldn't be.
"With an event like this dinner, they can fund much of a general election campaign in one evening. It is much harder to get thousands of smaller donations from the public. Labour is at fault, too, and also hosts fundraising events where you have to pay for a ticket, and who is sitting at the table is not declared."
Tamasin Cave, director of Spinwatch, a lobbying campaign group, said the summer parties were "a straight-up case of cash-for-access. Buying a seat at a minister's table provides these bankers, foreign businessmen and lobbyists with an opportunity to discuss their concerns, whether its taxes, regulation or policy".
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