Boris Johnson has declined to deny allegations that he failed to declare potential conflicts of interest as London mayor over the allocation of public money to a model turned technology entrepreneur.

The Prime Minister repeatedly refused to comment on allegations centring on his association with Jennifer Arcuri, during sustained questioning on his flight to New York for the United Nations General Assembly.

The Sunday Times reported that Ms Arcuri, an American who moved to London seven years ago, was given £126,000 in public money and was treated to privileged access to three foreign trade missions led by Mr Johnson.

The PM declined to clarify the nature of his relationship with the woman and declined chances to deny any allegations in the report.

First asked on board the RAF Voyager whether he would refute the claims, he said: “I’m here to talk about what we are doing in the UN and this country’s commitment to tackling climate change stopping the loss of biodiversity and our role as serving as a bridge between our European friends…”

He did not directly respond to six questions, including whether the allegations could be solved with a public enquiry.

When asked to clarify the nature of their relationship, he replied: “If you will forgive me we are going to talk exclusively about what we are doing here in the UN.”

Shadow minister for the Cabinet Office Jon Trickett has called for the PM to fully explain the matter.

“Boris Johnson must now give a full account of his actions in response to these grave and most serious allegations of the misuse of public money in his former role as mayor of London,” the Labour MP said.

“The public has a right to know how and why these funds were used for the benefit of a close personal friend without on the face of it legitimate reason.”

Ms Arcuri, 34, did not comment to the Sunday Times about the nature of her relationship with the PM.

“Any grants received by my companies and any trade mission I joined were purely in respect of my role as a legitimate businesswoman,” she said in a statement to the paper.

The newspaper investigation reported that Ms Arcuri’s business received £10,000 in sponsorship from an organisation overseen by Mr Johnson as mayor in 2013.

A further £15,000 was said to have come in 2014 and a £100,000 grant from the Department of Digital, Culture, Media and Sport earlier this year.

Downing Street has declined to comment.