City of London Police are considering investigating Adam Werritty, the close friend of former defence secretary Liam Fox, for possible fraud.
Labour MP John Mann has asked the police to probe allegations Mr Werritty used business cards falsely claiming he was an adviser to Mr Fox.
At the same time a firm he set up was receiving money from several wealthy supporters, it has been reported.
Mr Fox resigned after pressure over his working relationship with Mr Werritty.
A City of London Police spokesman confirmed they had received an allegation of fraud.
"Officers from the force’s economic crime directorate will consider the matter and establish whether or not it is appropriate to launch an investigation."
Mr Mann said he was also considering asking the Electoral Commission – which regulates political parties and their funding – to consider whether Mr Fox should face criminal proceedings over a failure to declare political donations.
The latest comes after venture capitalist Jon Moulton on Friday said Mr Fox approached him after the election seeking funds for Pargav – a non-profit company set up by Mr Werritty.
Mr Moulton said he was told Pargav was involved in "security policy analysis and research".
The Sunday Telegraph reported that some of the rich donors to the company were furious at being drawn into the row and had complained they were misled about the use of the funds they were providing.
Report due
Mr Fox’s conduct is being investigated by Cabinet Secretary Sir Gus O’Donnell, and a report is due to be published early next week.
It is expected to be very critical of his actions.
The defence secretary had been under intense pressure last week after it emerged that Mr Werritty had met Mr Fox 22 times at the MoD and joined him on 18 overseas trips since he came to office last year – despite having no official role.
Mr Werritty, a former flatmate of Mr Fox and the best man at his wedding, handed out business cards suggesting he was his adviser and was present at meetings Mr Fox had with military figures, diplomats and defence contractors.
Questions have been raised about who paid for Mr Werritty’s business activities and whether he had personally benefited from his frequent access to the defence secretary.
The BBC understands officials at the Department for International Development had raised concerns about Mr Werritty’s involvement in Sri Lanka where, it is claimed, defence contracts were being touted.
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