Ken Livingstone was paid an £8,000 fee by a hedge fund to entertain its clients, I have learned.
The disclosure will open him to the charge of gross hypocrisy, following his savage criticism of the Labour MP Dan Jarvis for taking a £16,800 political donation from the hedge fund manager Martin Taylor of Nevsky Capital.
Mr Livingstone described that donation as being like "Jimmy Savile funding a children's group" - an attack described by the former minister and Labour MP Alan Johnson as "outrageously stupid" and by the Labour MP Ian Austin as "disgusting".
But it turns out that on September 24th 2008, after being succeeded as London Mayor in May, Ken Livingstone gave a talk for the large and successful hedge fund Meditor on the top floor of the Gherkin tower in the City of London.
Meditor was a Bermuda-based hedge fund, with $3bn of assets, which was closed at the end of 2013.
Mr Livingstone was the keynote speaker at the firm's tenth anniversary party. His fee for the speech was £8,000.
According to a well-placed source, there were about 100 guests, including the hedge fund's clients and the investment banks it bought services from, such as Credit Suisse and Morgan Stanley.
I am told Mr Livingstone gave an amusing and upbeat speech about the resilience of the City of the London - even though he was speaking nine days after the collapse of the huge US investment bank Lehman Brothers.
The founder of Meditor, Talal Shakerchi, was much less optimistic in what he said to his clients at the party.
The disclosure that Mr Livingstone was employed to give this talk by a large hedge fund will be seen as making it all the more odd that he explained his analogy between hedge fund managers and the child abuser Savile by remarking:
I'm saying to Dan Jarvis if you want to be a serious player in the Labour party, don't mix with these people [hedge fund managers], they're sick.
I approached Mr Livingstone for a comment, but he did not return calls.
Mr Livingstone is an enthusiastic supporter of the Labour leader Jeremy Corbyn. Dan Jarvis is the current darling of the right and centre of the Labour party, and seen as a potential future challenger for the Labour leadership.
I have just spoken to Ken Livingstone and asked him whether he was guilty of double standards, in savaging Dan Jarvis for taking a political donation from a hedge fund, in spite of having himself received £8000 for speaking to the clients of a leading hedge fund.
"Not double standards" he said. "Different standards".
Mr Livingstone says he would have told the room of the need for the City to invest more in the economy, and it was irrelevant that he personally profited to the tune of £8000.
Some may not understand why it is acceptable to Mr Livingstone to take money personally from a hedge fund, but not take a political donation from a hedge fund manager.
He said he can't remember what he did with the money, though he pointed out that he has a history of donating money from his commercial activities to political causes.