The treasurer of the Conservative Party was accused last night of breaking parliamentary anti-sleaze rules after arranging to host a private dinner in the House of Lords for paying American Express card-holders.

Lord Fink arranged the event, which was part of a $10,000-per-head "Wimbledon Championships" package available to AmEx Platinum and Centurion card-holders, an investigation by the Bureau of Investigative Journalism and The Independent has found.

Advertised on the AmEx website as a "one-of-a kind opportunity to advance your lifestyle", the $9,391 (£6,000) package offered two full days of tennis, accommodation in the Dorchester, a drinks reception with John McEnroe – and the House of Lords dinner.

Yesterday, after being contacted, Lord Fink – who is David Cameron's chief fundraiser, and described as "the Godfather" of the hedge fund industry – said he had cancelled the booking after being made aware that it could break the rules. He said he had no financial interest in AmEx and had received no benefit from the booking. Lord Fink is one of a number of senior peers who have used their membership of the House of Lords to arrange events for private companies – some of whom do have a financial interest in the functions that are put on. They include:

* The former Metropolitan Police Commissioner Lord Stevens of Kirkwhelpington, who hosted a "customer event" for 140 people in the peers' dining room for a private forensic science firm of which he is a non-executive director and shareholder.

* The Tory peer Lord Sheikh, who booked the House of Lords Terrace overlooking the Thames for the launch of his own insurance broking firm.

The revelations form the first part of an investigation by the Bureau and The Independent into the workings of the House of Lords.

Lords rules state that banqueting facilities "are not to be used for the purposes of direct or indirect financial or material gain by a sponsor ... or any other person or outside organisation".

Lord Fink booked the event in the Attlee Room to coincide with this year's Wimbledon tournament.

He was nominated to the House of Lords last year, is one of the Tories' biggest donors and has been a guest of David and Samantha Cameron at Chequers. He became sole treasurer of the Conservative Party earlier this year when his predecessor, Peter Cruddas, was forced to resign after being secretly recorded "selling" dinner in Downing Street with David Cameron in return for donations to the party.

The revelation that Lord Fink was prepared to "sponsor" the luxury AmEx package, which was marketed to wealthy Americans visiting London, will be embarrassing to the party.

A spokesman for the House of Lords said: "The House of Lords has clear rules on the use of banqueting facilities.

"A breach of the rules constitutes a breach of the House of Lords Code of Conduct. It is a Member's own responsibility to ensure any event they sponsor does not contravene the rules in any way. There is also a robust mechanism in place for investigating alleged breaches of the Code of Conduct."

Tim Farron, the Liberal Democrat president, said: "This is further evidence of the urgent need for radical reform of the House of Lords.

"It has become as much a House of Lobbyists as a House of Lords. Our upper chamber has become packed with unelected political appointees who get £300 a day just for turning up.

"In the light of yet more scandal in our discredited political system, it is high time we introduced a smidgen of democracy and accountability into the upper house."

Labour said that the episode left "a very nasty taste" and called on Lord Fink to consider his position as Tory treasurer. "This is an attempt to breach the rules of Parliament," said Jon Trickett, the shadow Cabinet Office minister. "It leaves a very nasty taste to suggest that you can buy access to the House of Lords, and it cheapens democracy. Lord Fink, who is a major donor to the Tories, should consider his position as treasurer of the Conservative Party."

After being contacted, both Lord Fink and American Express said that they were cancelling the event which they said had been booked in good faith.

Lord Fink said: "This event has been held in the Lords on several occasions in the past and I agreed to sponsor it this year in return for a sizeable charitable donation to a major hospital.

"I have no commercial interest in AmEx and there was never any question of me profiting from sponsoring it." The donation to the hospital was £3,000.

A Conservative Party spokesman said: "Lord Fink cancelled his sponsorship of the event at the beginning of last week as soon as he received advice that there might be an issue with it."

American Express said: "We have re-examined the current House of Lords event and hospitality guidelines and consulted again with Lord Fink.

"We agreed that some of these guidelines are open to interpretation. In particular, the guidelines state, 'events may not be used for ... commercial business, although events related to charities are permitted'.

"Although the dinner planned for the House of Lords did have a charitable component it was not a fundraising event. We have therefore mutually agreed to hold the dinner at another location."

American Express said it would still make its planned charitable donation to St Thomas's Hospital, of £3,000.

Asked about Lord Stevens's sponsorship of the LGC reception, a spokesman said: "This was not a promotional event. Those attending would have no responsibilities for procuring our services."

Lord Sheikh said the launch of MacMillan Sheikh at the House of Lords was a social gathering which was "in no way intended as a source of business development in any shape or form" and that business was not discussed. He also denied that he had received payment from MacMillan Sheikh, despite being a director and chairman of the company.

The rules: no access for profit

House of Lords rules on the use of its premises and facilities for outside events are clear.

The rules say functions must not be used for the purposes of "direct or indirect financial or material gain by a sponsor ... or any other person or outside organisation".

This means that members of the Lords should not receive payment or any other kind of benefit, such as an offer of employment based on the ability to provide access to House of Lords.

Companies or organisations must not use functions to drum up business or as a perk for existing clients or shareholders.

Members may not sponsor promotional functions for companies in which they have a direct financial interest, such as a paid directorship or a substantial shareholding.