Inquiries at City Hall and Parliament into US businesswoman Jennifer Arcuri and her links with Boris Johnson will start jointly on Wednesday.
Tech entrepreneur Ms Arcuri is at the centre of allegations that the Prime Minister showed her favouritism by giving her £126,000 in public funding and privileged access to three foreign trade missions while he was mayor of London.
The London Assembly will discuss its investigation on Wednesday at 2pm after Mr Johnson complied with a request for evidence from the oversight committee.
Members of the committee have so far agreed with a request from the Conservative Party leader’s solicitors for the submitted papers to be kept confidential.
Only a few miles downstream, MPs will at the same time quiz Culture Secretary Nicky Morgan about a £100,000 grant that the Department of Digital, Culture, Media and Sport gave Ms Arcuri’s business.
There were questions raised in the Commons about the due diligence made on the grant approval after ministers justified awarding the money – meant to be spent on improving IT skills in the UK – because the company had a British phone number.
Calls to the number were answered by workers based in California, where Ms Arcuri, 34, is said to be based.
The culture committee will question the Secretary of State in the House of Commons at the same time as City Hall proceedings are getting under way.
Mr Johnson has previously accused his “old friends” in the Assembly of “barking up the wrong tree” with their investigation.
Ms Arcuri, a former model, used an interview with ITV’s Good Morning Britain to deny reports that she received favouritism during his eight-year stint as mayor.
The businesswoman, who said she met Mr Johnson for the first time in October 2011, has refused to comment on whether they had a romantic relationship as well as a professional rapport.
She said: “I think it’s quite unfortunate that it becomes that a good friend, who has now been, you know, now I’m dragged into the middle of this horrific scandal, you know, and the answer that I’m going to give is now going to be weaponised against this man.
“It’s really categorically no-one’s business what private life we had, or didn’t have. But – and categorically more important – Boris never, ever gave me favouritism.
“Never once did I ask him for a favour. Never once did he write a letter of recommendation for me. He didn’t know about my asking to go to trips.”