BORIS Johnson’s conduct while he was mayor of London is again under the spotlight after Jennifer Arcuri admitted to a four-year affair with the Prime Minister.

The US businesswoman, who received more than £100,000 of taxpayers' money, says the affair lasted from 2012 to 2016.

Johnson, who was serving in his second term as mayor, was married to his ex-wife Marina Wheeler during that period.

The Tory leader is currently being investigated by the Greater London Authority over suspicions he breached the Nolan Principles of Public Life.

The probe will examine whether he behaved with “honesty and integrity”, whether Arcuri was given “preferential treatment” and if there was any conflict of interest which should have been declared.

Johnson spoke at a series of technology events organised by the US businesswoman, who went on to receive £126,000 of taxpayers’ money in event sponsorships and grants.

Arcuri maintains she was invited on trade trips in her own right as a member of the London tech-scene “ecosystem”.

The National: Jennifer Arcuri

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Confirming the affair for the first time in an interview with the Sunday Mirror, the American said the pair met up at her flat in Shoreditch – where she had previously claimed to merely have provided “technology” lessons.

“I loved him. I adored him,” Arcuri told the paper, explaining they had a mutual “physical and intellectual attraction”.

But the Prime Minister was also branded a “cowardly wet noodle” for failing to stand up for her amid suggestions of favouritism.

She said: “It’s embarrassing. What a child. You can’t get on the phone and say, ‘Look Jen, this is crazy, welcome to politics’?

"He just took the most cowardly, wet noodle of approaches. This is who he is and it’s about time we recognised that.

“A great leader is charismatic, courageous and brave. None of these words I would use to describe Boris Johnson.”

The businesswoman claimed she wasn’t fully aware of the rules surrounding trade trips when she attended, but now believes Johnson should have declared the friendship.

“I would have seen no reason why he shouldn’t declare me,” she added.

Number 10 declined to comment.