The Conservative Party treasurer is to face a full Parliamentary inquiry into allegations that he broke anti-sleaze rules.
The Independent and the Bureau of Investigative Journalism revealed earlier this month that Lord Fink, who has given more than £2m to the Tories, sponsored a private dinner in the House of Lords for paying American Express cardholders.
Up to 60 paying guests were due to take part in the money-making dinner as part of the $10,000 Wimbledon Championships package available to AmEx Platinum and Centurion card holders. Under House of Lords rules members cannot sponsor functions designed to make money for private enterprises.
The dinner was cancelled after Lord Fink was contacted by the Bureau.
Lord Fink admitted that he had offered to sponsor the American Express dinner, part of a money-making package for the company. But there was never any possibility of him profiting, he said, and American Express planned to make a charitable donation.
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". Yesterday House of Lords Commissioner for Standards Paul Kernaghan wrote to Labour's shadow Cabinet Office Minister Jon Trickett to confirm that he was to carry out a full investigation into the breach.
He wrote: "I have now carried out a preliminary assessment of your complaint and have decided that a formal investigation is appropriate. I will in due course submit a report to the House of Lords Sub-committee on Lords conduct. I will ensure that you are advised of the outcome of my investigation."
The House of Lords Committee for Privileges and Conduct, can censure members who are found to have broken the code. Penalties can include a formal reprimand or, in extreme cases, suspension from the House of Lords until the following election.
Mr Trickett said the decision was the right one. "It is vital that Lord Fink's actions are fully investigated in order to uphold the credibility and reputation of Parliament and prevent any potential further breaches of the House of Lords Code of Conduct," he said. "It is vital that this formal investigation provides answers to key questions, in particular whether Lord Fink used his position to provide access to the House of Lords as part of a paid-for corporate package and giving the damaging impression that you can buy access to the House of Lords.
"I hope the Commissioner will use this formal investigation as an opportunity to shine a light on to the hidden and often murky world of business interests in the House of Lords."
The Liberal Democrat Peer Lord Oakshott added: "There is only one way to stop us being a house of donors and cronies and that is election by the people."