Dominic Cummings claims he was in the room when Boris Johnson was warned off giving a peerage to Evgeny Lebedev.
Mr Johnson's former chief aide accused deputy PM Dominic Raab of inadvertently misleading MPs by branding the clams "nonsense" at PMQs.
At PMQs, Labour's Angela Rayner demanded to know if the Prime Minister challenged security services advice to give his pal Evgeny Lebedev, media mogul and son of ex-KGB agent Alexander, a peerage in 2020.
She said the “close personal friend” of the Prime Minister gave him “thousands of pounds of gifts” and “champagne and caviar”.
But Deputy PM Dominic Raab failed to answer the question - instead angrily branding her claims “sheer nonsense”.
Mr Johnson himself has insisted it is “simply incorrect” that he personally or directly asked for the advice to be reversed.
But writing on his paywalled Substack blog, Mr Cummings said he had been in the room when Cabinet Office officials informed Mr Johnson about the concerns.
"I supported these concerns and said to the PM in his study explicitly that he should not go ahead," he wrote.
"He was very cross and as he does when cross he blustered nonsense.
"‘This is just … You’re just … [pause] ANTI-RUSSIAN!’"
Mr Cummings went on to claim Mr Johnson had done "his usual trick when I told him not to do something dumb" and got a "stooge" to "cut a deal" with someone in the Cabinet Office.
He added: "There was a handful of people in the room who were part of this discussion at least two of who would agree with my version in court.
"I’m confident in predicting nobody would swear under oath the PM is telling the truth — including the PM!"
At PMQs, Mr Raab said: "“All individuals nominated for a peerage are done so in recognition of what their contribution is to society.
“That includes those of Russian origin who contribute brilliantly to our nation, many of whom in this country are critics of the Putin regime.
“Peerages are vetted by the House of Lords Appointments Commission (HOLAC) for matters of probity and frankly she should know better.”
