It leases the space from Regus, a co-working firm which rents offices or even just a single moveable hot-desk by the hour, day or month.
Clients do not need to actually physically use the building if they do not wish – but can register there to get post delivered.
Hacker House was not on the handwritten tally of firms as renting office space in the building. But it was listed on the Regus computer systems.
The Department for Digital, Culture, Media and Sport (DCMS) is investigating the circumstances surrounding the grant.
Johnson has said “everything was done with complete propriety” while he was London mayor, and declined to clarify the nature of his relationship with Arcuri, and declined the opportunity to deny any allegations in the Sunday Times report.
Arcuri, 34, told the Sunday Times in a statement: “Any grants received by my companies and any trade mission I joined were purely in respect of my role as a legitimate businesswoman.”
The newspaper reported that another business belonging to Arcuri – Innotech – first received £10,000 in sponsorship from London Partners, the mayor’s promotional agency, in 2013.
A further £15,000 was said to have come in 2014 under a government programme designed to encourage foreign entrepreneurs in the UK.
Then her firm Hacker House was given a £100,000 cyber skills grant from DCMS earlier this year.
Hacker House has been contacted for comment.