It was an eclectic guest list. A Swiss-born banker and passionate Eurosceptic, a Christian hedge-fund boss who champions family values and the head of an international oil-trading firm who had played a vital role in helping fund the Libyan rebels fighting Muammar Gaddafi.

On a cold night last November the three men and their wives went through the famous Downing Street door, past the state rooms where guests are normally entertained and up to the more intimate surroundings of David and Samantha Cameron's top-floor flat.

The next day Mr Cameron was to travel to Cannes for the G20 summit. But this was one "social dinner" – as Downing Street insisted on referring to it yesterday – that the Prime Minister needed to fulfil. Between them, his guests had given or loaned the Conservative party more than £7m. It would not be an exaggeration to suggest that without their money he would not be in Downing Street himself. And if it had not been for the recent indiscreet boastings of the Tories' former treasurer, Peter Cruddas, the dinner – along with three other similar gatherings at No 10 and five lunches at Chequers – would never have come to light.

Now Mr Cameron faces awkward questions about the extent to which money can provide access to the Government and how much he is influenced by those who hold the purse strings of his party. Perhaps the most curious invitee at the Downing Street dinner was Ian Taylor, who gave the Tories £50,000 in 2009.

Mr Taylor is head of Vitol, the world's biggest oil dealer, who in the months leading up to the November dinner had played a vital role in helping Libyan rebels by supplying them with gasoline for their vehicles and selling Libyan crude oil for them on the international market. The arrangement – worth over £500m – had already caused controversy after it emerged that the deal had been brokered with the help of Alan Duncan, the International Development minister, who had received political donations from Mr Taylor.

Downing Street would not say yesterday whether Libya was discussed – but given that Colonel Gaddafi had been killed less than two weeks earlier it would seem likely. Mr Taylor is also on record as saying he expects his company "to play a role in the future [of Libya's oil industry]."

The other guests at the Downing Street dinner also had personal or business interests in Government policy.

Henry Angest – who attended the November gathering with Mr Taylor – controls a company that loaned the Tories £5m to help fund the last general election campaign. Reportedly worth £45m, the Swiss-born banker is a trenchant critic of attempts to impose greater regulation on the City. He is critical of the UK's "punitive tax system", which was softened last week.

Michael Farmer, a metals trader who has donated over £2m to the Conservatives since 2002, is a Christian and strong campaigner on family values – a cause Mr Cameron has championed. Mr Farmer has said that he does not feel that access has bought influence. "I'm a great believer in the family unit being a basic unit on which the rest of society can build itself," he told Parliament. "I personally don't think anything I have said has really influenced things too much. From the point of view of family policy I think this Coalition has really done nothing so far."

Then there is Michael Spencer, head of ICAP, the biggest broker of financial transactions in London, who had lunch at Chequers in 2010 and was invited to Downing Street for dinner just last month. He is on the record as saying that his firm would leave London if the Government agreed to a European proposal for a Financial Transaction Tax.

Early last month he gave an interview to a financial services magazine in which he said: "I have had it first-hand from very senior members of our administration who I know personally... that it will be vetoed without any doubt and without any reservation at all."

PRIVILEGED ACCESS: CAMERON'S GUESTS