Boris Johnson has been referred to the police complaints body for England and Wales to assess whether he should face a criminal investigation over his links with American businesswoman Jennifer Arcuri.
The Greater London Authority (GLA) said its monitoring officer had recorded a "conduct matter" against Mr Johnson over allegations Ms Arcuri received sponsorship monies and access to trade missions because of her friendship with him while he was mayor of London, reports Telegraph UK.
The Independent Office for Police Conduct (IOPC) will now consider whether there are grounds to investigate the Prime Minister for the criminal offence of misconduct in public office.
Mr Johnson has denied any wrongdoing in relation to his friendship with Ms Arcuri.
Earlier he said that he would comply with an order by the London Assembly to provide details of his links with Ms Arcuri, although he insisted they were "barking up the wrong tree".