Boris Johnson has insisted there was "no interest to declare" amid claims about his association with former American model turned tech businesswoman Jennifer Arcuri.
Asked by the BBC’s Andrew Marr if he declared an interest relating to his links with Ms Arcuri when he was London mayor, the PM replied: "Everything was done in accordance with the code ... and everything was done with full propriety."
Pressed again, Mr Johnson said: "There was no interest to declare...
"Let's be absolutely clear, I am very, very proud of everything that we did and certainly everything that I did as mayor of London.
"I may say that the current mayor of London could possibly spend more time investing in police officers than he is investing in press officers and peddling this kind of stuff."
It follows reports that Ms Arcuri told friends that she had an affair with Mr Johnson while he was mayor of London.
On Friday, the Prime Minister was referred to the police complaints body to assess whether he should face a criminal investigation over his links with former model Jennifer Arcuri.
The Sunday Times has now reported that she confided to four friends that they had been engaged in an affair during his time in City Hall.
The paper said that David Enrich, now the finance editor of The New York Times, had said he had been told of the alleged relationship by two of her friends when he was working for another newspaper.
His account was said by the Sunday Times to corroborate that of other sources who had spoken to Ms Arcuri.
Downing Street refused to comment on the report.
The claims come after the Greater London Authority (GLA) said its monitoring officer had recorded a "conduct matter" against Mr Johnson over allegations Ms Arcuri received favourable treatment because of her friendship with him while he was mayor of London.
The Independent Office for Police Conduct (IOPC) is now considering whether there are grounds to investigate the Prime Minister for the criminal offence of misconduct in public office.
The GLA statement, denounced by Downing Street as a "nakedly political put-up job" on the eve of the Tory Party conference, came after details of Ms Arcuri's links to Mr Johnson were first highlighted in the Sunday Times last week.
The newspaper reported that Ms Arcuri was given £126,000 in public money and privileged access to three foreign trade missions led by Mr Johnson while he was mayor.
Mr Johnson has consistently denied any wrongdoing in relation to his links with Ms Arcuri.
Health Secretary Matt Hancock dismissed the claims surrounding Mr Johnson's relationship with Ms Arcuri as a "squall".
Asked on Sky News's Sophy Ridge on Sunday programme if the Prime Minister had questions to answer, Mr Hancock replied: "No."
He went on: "My understanding is that there is an investigation. Any monies involved went through proper due process. This was a long time ago.
"Of course, in politics, there is always squalls and there are always debates about individuals."