BORIS Johnson will not be the subject of a criminal investigation by the police watchdog over allegations that he used his position while London mayor to benefit and reward US businesswoman Jennifer Arcuri.

The Independent Office for Police Conduct (IOPC) said that it would not be launching a probe into the Prime Minister following claims of misconduct in public office, which he denies.

But the London Assembly said it will resume its own investigation into allegations that Arcuri received thousands of pounds in public money and privileged access to three foreign trade trips led by Johnson when he headed City Hall.

Neither the PM nor Arcuri have denied that they were involved in an affair.

The allegations were referred to the IOPC in September because the watchdog has a remit over the City Hall role, as head of the mayor's office for policing and crime.

Now the result of a months-long scoping exercise by the IOPC has concluded that a criminal investigation should not go ahead.

But the London Assembly said it would resume its own investigation, which it paused at the request of the police watchdog.

READ MORE: Jennifer Arcuri asks Boris Johnson for apology over 'humiliation'

Len Duvall, chairman of the Greater London Authority's oversight committee, said: "The IOPC was looking specifically at whether he committed a criminal offence. That's not our remit and their decision doesn't have any real bearing on our investigation, which will focus on his conduct as mayor of London."

The Labour assembly member added: "Everyone who holds public office, whether you're the mayor of London, or indeed the Prime Minister, is expected to adhere to the principles of public life - including integrity, selflessness, openness and honesty, to name a few.

"Our investigation will consider whether Boris Johnson conducted himself in a way that's expected from anyone in that position."

The allegations surfaced in an investigation by the Sunday Times on September 22 last year, on the morning the PM was flying to New York to attend the United Nations General Assembly.

Initially he declined to deny any of the claims during sustained questioning on the RAF Voyager, but later broke his silence to insist "everything was done with complete propriety".

Arcuri has said she had "every right" to go on the trade missions, describing herself as a "legitimate businesswoman".

A Government review in October said a separate £100,000 grant awarded to Hacker House, a company run by Arcuri, in 2018 was "appropriate".

The newspaper investigation reported that Arcuri's business received £10,000 in sponsorship from an organisation overseen by Johnson as mayor in 2013 and a further £15,000 was said to have come in 2014.