UK Prime Minister Boris Johnson has denied any wrongdoing over his links to an American businesswoman who allegedly received public money and favourable treatment because of their friendship during his time as London mayor.

Last week the Greater London Authority referred Mr Johnson to a police watchdog agency over allegations he had a conflict of interest arising from his close relationship with Jennifer Arcuri.

The UK Prime Minister says "there was no interest to declare" in his dealings with Ms Arcuri, described by the UK press as a former model, who has set up several IT businesses in London since 2012.

Here's what we know about the matter.

Who is Jennifer Arcuri?

Jennifer Arcuri describes herself as an "entrepreneur, cybersecurity expert and producer". ( Supplied: YouTube/ Tedx Talks )

According to her IMDb profile, the American businesswoman started her career as a DJ at Radio Disney and worked in the film industry, including producing a short film that was shown at the Cannes Film Festival.

On her Twitter profile, she describes herself as an "entrepreneur, cybersecurity expert and producer".

Ms Arcuri, 34, first met with Mr Johnson in 2012 after he delivered the first keynote speech at a technology policy discussion series she founded, known as Innotech.

She has since founded a firm in London called Hacker House, which promotes "ethical hacking" to help businesses boost their cybersecurity.

Ms Arcuri has delivered several public lectures on cyber skills and ethical hacking, including TED talks on YouTube.

Hacker House is facing an investigation over its eligibility for a cyber skills grant from the UK government, worth 100,000 pounds and meant for UK-based businesses, after Ms Arcuri and her husband relocated to California in 2018 and only continued operating a "virtual office" in London.

Ms Arcuri has made few comments about the allegations but told the Guardian: "The stories you are writing are more and more false. These are fake news."

How is Boris Johnson involved?

UK Prime Minister Boris Johnson is being investigated by the police watchdog over claims of a conflict of interest. ( AP: Kirsty Wigglesworth )

The Sunday Times reported that Ms Arcuri attended trade missions Mr Johnson led to the United States, Israel and Asia, even though her fledgling business had not yet met eligibility requirements for such trips.

In 2013, Innotech received 10,000 pounds in sponsorship from a fund overseen by the London mayor.

The Sunday Times also reported that Ms Arcuri had told four friends that she had an affair with Mr Johnson while he was mayor, but neither of them has commented on these allegations.

He is also accused of having been a frequent visitor to Ms Arcuri's apartment in Shoreditch during his tenure as mayor.

The conflict of interest matters have been referred to the Independent Office for Police Conduct, as Mr Johnson served as London's police commissioner between 2008 and 2016.

What does the UK PM say?

Mr Johnson has denied any wrongdoing and suggested that political motivations were behind the allegations.

He described the referral by the Greater London Authority as a "nakedly political put-up job" and attempted to lay the blame on current Mayor Sadiq Khan.

"Everything was done in accordance with the code … and everything was done with full propriety," Mr Johnson told the BBC.

When pressed again by BBC journalist Andrew Marr, Mr Johnson added: "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," he said, adding that Mr Khan "could possibly spend more time investing in police officers than he is investing in press officers and peddling this kind of stuff".

AP/ABC