American businesswoman Jennifer Arcuri reportedly told friends about an affair with Boris Johnson during his time as mayor of London.
The prime minister was referred to the police complaints body on Friday, to assess whether he should face a criminal investigation over his links with the former model.
The Sunday Times has now reported that Arcuri confided in four friends about an affair she had been engaged in with Johnson 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.
His version of events was said by the Sunday Times to corroborate with information from other sources who had spoken to Arcuri.
Downing Street has 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 the prime minister over allegations 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 Arcuri’s links to Johnson were first highlighted in the Sunday Times last week.
The newspaper reported that Arcuri was given £126,000 ($AU 229,489) in public money and privileged access to three foreign trade missions led by Johnson while he was mayor.
Johnson has consistently denied any allegations of wrongdoing in relation to his links with Arcuri.
Enrich told The Sunday Times that he had been working on an article on Arcuri’s business partner for the Wall Street Journal, published in 2013, when he interviewed her and spoke to a number of people in her close circle.
He told the paper: “Two friends from her business class said they had been told by Arcuri that she was sleeping with Boris. They told me that before and after that story ran.”
The latest allegations of infidelity follow a string of well-publicised stories involving Johnson’s private life, some of which plagued his 25 year marriage to second wife Marina Wheeler.
In 2004 he was sacked from the Tory frontbench over a reported affair with journalist and colleague at the Spectator Petronella Wyatt.
He described claims about the relationship as “an inverted pyramid of piffle” at the time.
Further claims surfaced in 2006 when it was reported that the married father-of-four had been romancing Anna Fazackerley of the Times Higher Education Supplement.
The Appeal Court ruled in 2013 that the public had a right to know that he had fathered a daughter during another adulterous liaison with another woman, Helen Macintyre, while mayor of London in 2009.
Despite surviving years of turmoil, Mr Johnson and his lawyer wife separated and began divorce proceedings in 2018 and he is now living at Downing Street with former Tory Party worker Carrie Symonds, 31.
Health secretary Matt Hancock described the allegations against the prime minister on Sunday morning as “squall”.
Asked on Sky News’s Sophy Ridge on Sunday programme if Johnson had questions to answer, 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.”