The US businesswoman embroiled in a conflict of interest row over her close friendship with Boris Johnson won a highly sought after entrepreneur visa to stay in the UK after securing the prime minister’s endorsement for her firm, the Guardian has learnt.

Jennifer Arcuri, whose company is being investigated over its eligibility for a £100,000 taxpayer-funded grant, spoke publicly of her difficulties in obtaining a visa.

But just months after Johnson helped to raise her firm Innotech’s profile by giving keynote speeches at two of its first events, Arcuri won a place on a prestigious government-run visa scheme, giving her firm £15,000 in public funds.

Arcuri, whose flat Johnson reportedly frequented while he was London mayor, beat nearly 2,000 applicants to be among 200 winners of the Sirius scheme run by UK Trade and Investment (now the Department for International Trade).

Tier 1 entrepreneur visa applicants are normally required to have up to £200,000 available for investment, but Companies House records show Innotech has been consistently in the red since it was founded. Its first accounts in 2014 showed it had minus £41,540 in shareholders’ funds.

However, it is understood there was no such financial stipulation for recipients of visa via the Sirius programme.

The Guardian also understands that Arcuri attended an event hosted at Buckingham Palace by the Duke of York in December 2014. Her latest company, Hacker House, apparently later claimed to have the backing of Prince Andrew for a scheme providing cyber badges for children.

Contacted by the Guardian, Arcuri broke her week-long silence to declare: “The stories you are writing are more and more false. These are fake news.”

But when a reporter pointed out that government documents publicly available on the internet prove she was accepted on to the entrepreneur scheme months after Johnson promoted her business, asking her to clarify which part was false, she replied: “No comment.”

On Monday, Johnson stonewalled repeated questions about his friendship with 34-year-old Arcuri – first revealed by a Sunday Times investigation – as he visited New York for a UN summit. There is no suggestion Johnson intervened in helping Arcuri win the visa.

Arcuri first met the politician in 2012 after moving to the UK to study for an MBA. Johnson appeared at four events for Innotech, which organises summits for young technology entrepreneurs. In October 2013, Innotech received a £10,000 grant from London and Partners, which Johnson had oversight of as mayor. A further £1,500 was given by L&P to sponsor an event the firm held at parliament.

She relocated back to the US last June but her latest company, Hacker House, won a £100,000 cyber skills grant from the Department for Digital, Culture, Media and Sport earlier this year, which is now subject to an investigation by the department over whether the firm was eligible for the grant, which is only intended for UK-operating companies.

Arcuri spoke publicly after her struggles to obtain a visa in a Sunday Times interview in July 2013, telling the paper that she was nearly ready to pack up and go home to the US.

According to the story, she needed £200,000 of investment to remain in the UK, allowing her to apply for a tier 1 entrepreneur visa, giving her a three-year stay. She successfully won the money earlier that month, the article reported, quoting her as saying: “Most of us give up. We come here, spend a lot of money on studies and have to leave because it’s too tough.”

Months earlier, on 26 April 2013, Johnson attended an Innotech Summit, helping Arcuri promote her new venture and raise its profile. He said: “There are 24,000 tech business here in London: nanotech, fintech, biotech, greentech, Innotech. There are huge numbers of brilliant people coming here to London.”

And speaking at an Innotech event in 2012, Johnson said: “This is exactly the kind of entrepreneurship that I think is going to lead London, lead this country, out of recession. I hope very much that I can do everything in my power to encourage Tech City and everybody who works in it to flourish.”

The Sirius scheme helps provide visas for “international graduates with ambitions to start and grow a business … in the UK”. It said that “teams with ideas for a business or existing startups in the early stages should apply for this programme”.

A 2015 brochure for the scheme “introducing some of the world’s most talented graduate entrepreneurs” shows Arcuri’s Innotech successfully won a place after the visa programme was launched in July 2013. It stated: “Innotech Summit is the only event to bridge the gap between entrepreneurs, investors and policy-makers in order to stimulate the growth of tech clusters around the world.”

In May 2014, Arcuri spoke about how grateful she was for the visa. “I’m very thankful to the Sirius programme for allowing me to come to the UK … and to build a company to rock the world with!”

A former employee of Arcuri’s said: “She had visa problems, which is why she had to raise a certain amount of money in 2013 after completing her MBA.”

Meanwhile, according to a source, Arcuri attended an event at Buckingham Palace in December 2014 hosted by Prince Andrew. The event, Code Club at the Palace, was held for delegates of D5, a Cabinet Office-run summit bringing together “advanced digital governments and reinforc[ing] the UK’s position as a digital world leader”.

It was later claimed that Hacker House won the backing of Prince Andrew for a scheme that would award cyber badges to children.

Details of the prince’s endorsement were mentioned during an extradition hearing for Lauri Love – who met Arcuri in 2015 and worked for Hacker House. In June 2016, Love successfully fought extradition to the US over allegations that he stole huge amounts of data from government agencies. But the cyber badges scheme never got off the ground, according to a source.

Meanwhile, an interview given by Arcuri in 2016 mentioned that Hacker House was developing “cyber badges for schools, on request of the Duke of York, to understand the awareness and ethics of cybersecurity”.

Arcuri denied that Prince Andrew backed her firm but when asked to explain why it was mentioned in the article, she failed to respond.

A spokesman for the Duke of York declined to comment.

The Department for International Trade declined to comment.

• This story was amended on 2 October 2019 to clarify that there was no stipulation on the availability of investment funds for Sirius programme beneficiaries.