US Edition The senior minister without portfolio is one of three trustees of the Bilderberg Association, the organisation that funded the conference last week.
Mr Clarke told the Commons that he had “forgotten” that the controversial gatherings were paid for from funds raised by the group.
He said he was checking his records to see whether he had informed civil servants of his role, as would be expected to avoid potential suggestions of a conflict of interest.
Mr Clarke made the disclosure while answering questions over the “private” meeting of 140 of the world’s most powerful executives, politicians, ministers and advisers, which took place at a hotel near Watford last week.
The minister, who has been a member of the Bilderberg Group steering committee for 10 years, attended the annual event, along with David Cameron, George Osborne, Ed Balls and Lord Mandelson.
Mr Clarke attacked as “rubbish” the conspiracy theories swirling around the mysterious gathering, which was also attended by Christine Lagarde, the managing director of the International Monetary Fund, Eric Schmidt, executive chairman of Google, Bob Dudley, chief executive of BP, and Jose Manuel Barroso, president of the European Commission.
However, the senior Labour MP Tom Watson asked Mr Clarke whether he had declared his trusteeship of the body that funded last week’s meeting, the Bilderberg Association.
Mr Clarke replied: “I am looking that up because I had forgotten that I am actually a member of the steering committee.
“When we were hosting at Watford, I discovered that amongst other things, I am a trustee of the British steering group, so I am checking with the aid of my constituency secretary, whether I put that in.
“I had completely forgotten that the thing was set up on that basis,” he said.
“The trustees have never met as trustees. All I actually do is sit as a member of the committee and play my part in the organisation of a meeting and that is all I have ever done.”
Mr Clarke said he had never spoken before in the Commons “to answer questions on behalf of a private organisation for which the British government has absolutely no responsibility whatever”.
Those attending the meeting go there for an “off-the-record, informal discussion” but have no intention to “plot” or “decide anything", Mr Clarke said.
“With the greatest respect, this is total, utter nonsense,” he added.
The minister was answering an urgent question in the Commons from Michael Meacher, the Labour MP and former minister, who asked why no official statement had been made about the discussions at the meeting.