Lord Portsmouth was last night revealed as the peer who helped bankroll Mr Neil Hamilton's doomed libel action against Mr Mohamed Al Fayed.
The man who set up the fighting fund, Lord Harris of High Cross, said: "Yes, that's right. Lord Portsmouth was one of the biggest contributors to the fighting fund.
"He is a well known supporter and he's come forward now. He was the mystery man we called Q because we didn't want to use his name at all.
"Of course his real name's Quentin so the whole thing's rather splendid."
Mr Hamilton faces costs amounting to more than £2 million following his failed attempt to clear his name of accepting bribes from the Harrods' tycoon and yesterday said that, even after selling his two homes, he will not be able to raise enough to cover them.
Supporters of Mr Hamilton raised a £400,000 fighting fund to help him bring the case, and the High Court judge, Mr Justice Morland, yesterday gave him 28 days to hand over to Mr Al Fayed's lawyers a list of anyone who gave more than £5,000, so that they too can be pursued for costs.
Reports yesterday suggested other possible donors to the fund included columnist and playboy, Mr Taki Theodoracopulos, the author and former Tory MP, Mr Gyles Brandreth, and former Guinness Book of Records editor, Norris McWhirter.
Mr Hamilton said yesterday he felt like a "broken man" and would have to sell his £700,000 home in Cheshire and his flat in Battersea, south London, to make even a dent on his legal bills.