Boris Johnson has denied allegations from a female journalist that he squeezed her thigh under the table during a private lunch in 1999.
Charlotte Edwardes, a Sunday Times journalist, claimed the incident occurred at the offices of The Spectator magazine in London when the prime minister was its editor.
“Under the table I feel Johnson’s hand on my thigh”, she wrote in her column on Sunday. “He gives it a squeeze. His hand is high up my leg and he has enough flesh beneath his fingers to make me sit suddenly upright.”
Mr Johnson, who has refused to comment on the nature of his relationship with the US businesswoman Jennifer Arcuri, took the unusual move of rejecting the allegation. A Number 10 spokesman said: “This allegation is untrue.”
Ms Edwardes tweeted in response to No 10: “If the prime minister doesn’t recollect the incident then clearly I have a better memory than he does.”
Matt Hancock, the health secretary, told channel 4 news: “I know Charlotte well and I entirely trust what she has to say”.
The prime minister also faces a potential criminal investigation over his links with Ms Arcuri, who reportedly received grants and preferential access to trade missions while he was mayor.
City Hall has hit back at accusations of political bias after the Greater London Authority referred Mr Johnson to a policing watchdog over alleged sponsorship and favours granted to Ms Arcuri.
Mr Johnson suggested on Sunday that the probe into misconduct allegations about his friendship with Ms Arcuri, a technology entrepreneur, was politically motivated and was being driven by Sadiq Khan, the Labour politician who succeeded him as mayor.
The GLA monitoring officer — an ethics watchdog — announced on Friday that it had raised a “conduct matter” with the Independent Office for Police Conduct for possible investigation over misconduct in public office.
Asked on the BBC’s Andrew Marr show if he believed the allegations levelled against him were politically motivated, Mr Johnson said: “I think you’ve got to be realistic if you’re in my position. You’ve got to expect a lot of shot and shell.”
He added that Mr Khan, a former Labour MP, could “possibly spend more time investing in police officers than he is investing in press officers and peddling this kind of stuff”.
Senior City Hall officials pointed to the fact that the Arcuri process was being handled by civil servants at the GLA. A spokesperson for the mayor said: “This process is nothing to do with the current mayor. It is a decision by the independent monitoring officer for the Greater London Authority.”
Mr Johnson has denied any impropriety over his friendship with Ms Arcuri. Asked whether he had declared an interest to City Hall, Mr Johnson told the BBC there was no interest to declare.
He added: “Everything was done in accordance with the code, and everything was done with full propriety.”
In a letter sent to Mr Johnson and published alongside the GLA statement, the monitoring officer laid out the detail of the claims, which were first reported by the Sunday Times newspaper last week.
It said Innotech, Ms Arcuri’s then company, received £11,500 from London & Partners, the mayor’s promotional agency, for two events in 2013 and 2014. It added that Ms Arcuri was able in November 2014 to attend a trade mission to Singapore and Malaysia through Playbox, one of her companies, even though an initial application through Innotech had been declined.
In a statement last week, Ms Arcuri said: “Any grants received by my companies and any trade mission I joined were purely in respect of my role as a legitimate businesswoman.”