Boris Johnson’s response regarding his relationship with US businesswoman Jennifer Arcuri is “insufficient” and does not need to be kept secret, the London Assembly has said.
City Hall had given the Prime Minister 14 days to answer its questions over allegations the entrepreneur received favourable treatment while he was London mayor.
Mr Johnson responded on Tuesday evening, but his solicitors called for the evidence to be kept confidential.
But the Assembly has hit back, saying it could see “nothing” that “reflects the need for confidentiality” in the submitted papers.
Len Duvall, assembly member and chair of the oversight committee, said the Conservative Party leader had not answered all the questions regarding his relationship to Ms Arcuri.
The PM faces calls for clarity over allegations Ms Arcuri was given public funding and privileged access to three foreign trade missions while Mr Johnson was mayor.
Labour has also called for the PM’s response to be made public.
Mr Johnson has previously accused his “old friends” in the Assembly of “barking up the wrong tree” with their investigation.
Ms Arcuri used an interview on Monday with ITV’s Good Morning Britain to deny reports that she received favouritism during his eight-year stint as mayor.
Responding to the PM’s submission, Mr Duvall said: “We did finally receive a response from Boris Johnson, through his solicitors, which they have indicated may not be published.
“At this stage we are respecting that, but we are seeking further clarification.
“Nothing in the response, in our opinion, reflects the need for confidentiality. In fact, the response is insufficient as far as our request for information is concerned.”
The Assembly had asked him to provide details and a timeline of all contact with Ms Arcuri while he was the mayor.
It also asked him to give an explanation of how that relationship was disclosed and taken into account in all dealings with the assembly and related bodies.
Labour’s Mr Duvall said his committee was considering using “our power of summons” in order to hear Mr Johnson’s testimony in public, and confirmed a decision on what action they would take would be “finalised in the coming days”.
The Independent Office for Police Conduct (IOPC) is also conducting its own investigations into the allegations, he confirmed.
Labour said Mr Johnson should not be allowed to “hide from scrutiny”.
Jon Trickett MP, shadow minister for the Cabinet Office, said: “With an issue as serious as potential abuse of public office, it is absolutely in the public interest that this letter be published.
“Boris Johnson might think he is above the law but he cannot hide from scrutiny. As a former prime minister said, sunlight is the best disinfectant.
“If he fails to answer these questions, he is showing contempt for the inquiry and the people of this country. This is about the integrity and honesty of the man who is the Prime Minister.”
Despite the PM’s response on Tuesday, there was a spat between City Hall and those close to Mr Johnson over the deadline.
City Hall initially criticised him for missing the 6pm limit, with Mr Duvall warning the PM the situation had “now become grave”.
A Tory source hit back saying it “was an invented City Hall deadline that they have never said to us”, and criticised London Assembly “grandstanding” and Mr Duvall for “playing politics”.
The PM’s response was received about an hour after the deadline.
Those who fail to respond to Assembly summons for evidence can face up to three months in jail.