Prince Charles has “no knowledge” of his former aide’s alleged promise to help a Saudi billionaire secure a knighthood and a British citizenship, Clarence House has said.

Michael Fawcett, a trusted aide and former valet of the Prince of Wales, faces accusations that he would “support and contribute” to Saudi tycoon Mahfouz Marei Mubarak bin Mahfouz’s application for citizenship after the businessman donated to Charles’ charity, The Prince’s Foundation.

Fawcett has temporarily stepped down for his role as chief executive of The Prince’s Foundation over the claims, and an investigation has been launched into the allegations. According to the Sunday Times, Mahfouz has denied any wrongdoing.

A spokesperson for Clarence House said: “The Prince of Wales has no knowledge of the alleged offer of honours or British citizenship on the basis of donation to his charities and fully supports the investigation now underway by The Prince’s Foundation.”

Norman Baker, a former Liberal Democrat MP and author of a book on royal finances, wrote to the Metropolitan Police asking the force to investigate Fawcett.

A spokesperson for Scotland Yard said that police are “aware” of media reports about the issue and are waiting for “further contact in relation to this matter”.

In a letter written by Fawcett in 2017, seen by the Mail on Sunday, the royal aide offered to help Mahfouz with his citizenship application “in light of [his] ongoing and most recent generosity”.

The letter added: “I can further confirm that we are willing to make [an] application to increase His Excellency’s honour from Honorary CBE to that of KBE in accordance with Her Majesty’s Honours Committee.”

Mahfouz had previously been awarded a CBE by Charles in 2016 and is listed as a “community patron” on The Prince’s Foundation website.

A spokesperson for the charity said: “The Prince’s Foundation takes very seriously the allegations that have recently been brought to its attention and the matter is currently under investigation.

“The scope of The Prince’s Foundation investigation has been extended to cover this weekend’s newspaper reports. The Trustees had already arranged an independent review by an external senior forensic accountant from a ‘big four’ accountancy firm.”