Boris Johnson must explain his relationship with a businesswoman who was allegedly given preferential treatment during his time as Mayor, London politicians have said.

The London Assembly is concerned that the potential conflict of interest was not disclosed to the Greater London Authority (GLA).

Jennifer Arcuri, who was in her late twenties at the time, described the Prime Minister as “one of her best friends”, and he paid multiple visits to her Shoreditch flat, according to a report in The Sunday Times.

But Mr Johnson did not mention his relationship with the American business owner to the GLA – despite handing her thousands of pounds in sponsorship from City Hall.

Len Duvall, chairman of the London Assembly’s GLA Oversight committee, which scrutinises the workings of City Hall, yesterday wrote to the Prime Minister to express his “concern” at the allegations.

Mr Duvall demanded a timeline of all Mr Johnson’s dealings with Ms Arcuri during his time as Mayor, as well as an explanation of how disclosure of the alleged personal relationship was handled.

Ms Arcuri moved to the UK in 2011, after working in modelling and film production, and launched a company providing networking opportunities for the tech industry.

Innotech was given £10,000 in funding overseen by the Mayor in 2013, and Boris Johnson also spoke unpaid at a number of events promoting the company.

Ms Arcuri also received a £15,000 Government grant in 2014, and £100,000 from the Department for Digital, Culture, Media and Sport last year, from a round of funding intended for British businesses.

The entrepreneur now lives in California, but her grant application was linked to a UK address. The Government is investigating the grant.

The Sunday Times also claims Ms Arcuri received preferential treatment for overseas trade trips, with the Mayor’s team intervening to ensure she was selected as a delegate after her initial application was turned down on at least two occasions.

Under the GLA’s Code of Conduct, Mr Johnson was bound “to declare any private interests relating to public duties and to take steps to resolve any conflicts arising in a way that protects the public interest”.

The GLA Oversight Committee has requested a response from the Prime Minister within two weeks.