LONDON — A British police watchdog agency said on Thursday that it would not conduct a criminal investigation into Prime Minister Boris Johnson over claims that as mayor of London he had done official favors for an American businesswoman whose apartment he sometimes visited during working hours.
It also said there was “some evidence that Mr. Johnson and Ms. Arcuri may have been in an intimate relationship during some of the relevant time period.”
The decision does not spell an end to official investigations into Mr. Johnson’s conduct. An oversight committee of the London Assembly, an elected body, said it would now open its own inquiry, having earlier suspended it while the police watchdog, the Independent Office for Police Conduct, decided whether to investigate.
“The I.O.P.C. were looking at whether Boris Johnson had committed a criminal offense,” said Len Duvall, an opposition Labour Party lawmaker who is chairman of the oversight committee. “Our investigation will look at whether he conducted himself in a way expected of those in public office. My message to the prime minister is that this issue isn’t going away just yet.”
The police watchdog said it had faced significant hurdles in its inquiry, including that Mr. Johnson’s email account was irretrievably deleted by the Greater London Authority, the administrative body consisting of the mayor’s office and the London Assembly.
Mr. Johnson’s office criticized the inquiry, saying in a statement: “We welcome the fact that this politically motivated complaint has been thrown out. Such vexatious claims of impropriety in office were untrue and unfounded.”
Both Mr. Johnson and Ms. Arcuri have denied any wrongdoing.
It fed speculation about Mr. Johnson, whose turbulent personal life — he has been divorced twice, refuses to say how many children he has and was once fired for lying about an extramarital affair — has made headlines throughout his career.
Mr. Johnson’s fiancée, Carrie Symonds, gave birth to their baby boy last month, after she said she had experienced coronavirus symptoms and he was released from the hospital after a harrowing battle with Covid-19.
The investigation into his conduct as London’s mayor — an office that he held from 2008 to 2016 — centered on several payments and positions on trade missions given to Ms. Arcuri, a tech entrepreneur who was in her 20s when her path first crossed Mr. Johnson’s in 2011.
In 2013 and 2014, a promotional agency overseen by the mayor gave Innotech, Ms. Arcuri’s first venture after leaving business school, a total of 11,500 pounds, roughly $14,000. The Greater London Authority also gave her company a £12,447 grant in 2013 to attend a trade mission in South Africa, and Ms. Arcuri secured spots on trade missions led by Mr. Johnson to Malaysia, New York and Tel Aviv despite her being told at various points that she did not qualify.
The Sunday Times reported that Mr. Johnson had paid regular visits to Ms. Arcuri’s East London apartment, sometimes during afternoon work breaks. The Sunday Times later reported that Ms. Arcuri had told friends that she and Mr. Johnson were having a sexual affair, though she has since given ambiguous answers to questions from journalists about their relationship.
One witness told the police watchdog that Ms. Arcuri had spoken of having a sexual relationship with Mr. Johnson, the agency said.
The police watchdog said there was no evidence that Mr. Johnson had influenced the payments to Ms. Arcuri or that he had tried to help her secure spots on the trade missions. It did say, however, that it had evidence that the payments by the mayor’s promotional agency “were influenced by the decision makers’ belief that there was a friendship between Ms. Arcuri and Mr. Johnson.”
The watchdog cited two internal emails from the promotional agency. “We need friends like Jennifer,” one said. “Putting in good words for us with the Mayor is certainly in our interest.”
The other said that Ms. Arcuri was “very good at name dropping and has Boris eating out of her hand,” and added, “so we need to help where we can; as she’s prone to a whinge.”
The watchdog said that Mr. Johnson had not been obligated to declare his dealings with Ms. Arcuri. But it said that “if Mr. Johnson was in an intimate relationship with Ms. Arcuri, it would have been wise for him to have declared this as a conflict of interest.”
Ms. Arcuri declined to be interviewed by the police watchdog, but submitted written answers. The agency said those sometimes conflicted with email evidence showing, for example, that Mr. Johnson’s aides had a role in allowing her a spot on a trade mission.