Labour has called for the review into how Boris Johnson’s refurbishments of his Downing Street flat were financed to be expanded to investigate whether the public was misled over the renovations.

No 10 declined on Tuesday to deny suggestions that the Prime Minister received a loan from the Conservative Party to cover the initial costs, before repaying the party.

But that claim appears to run contrary to what Mr Johnson’s then press secretary Allegra Stratton said last month when she denied any party funds were used for refurbishments.

After Mr Johnson was accused of lying by Labour, deputy leader Angela Rayner urged Cabinet Secretary Simon Case to expand his review to investigate the comments.

She urged him to probe “whether the former press secretary knowingly misled journalists and the public, or was misled herself by senior members of the Government who seem intent on a cover-up”.

The Prime Minister was facing continued questions of how the works were paid for, after former aide Dominic Cummings said Mr Johnson wanted donors to “secretly pay” for the work in an “unethical, foolish, possibly illegal” move.

The Tories declined to deny a suggestion, first reported by ITV, that the Conservative Campaign Headquarters (CCHQ) paid the Cabinet Office to cover initial costs of the refurbishments, with Mr Johnson now repaying the party.

The Prime Minister’s official spokesman said: “Any costs of the wider refurbishment in No 10 have been met by the Prime Minister and he has acted in accordance with the appropriate codes of conduct and electoral law.”

He was pressed on a denial by the Prime Minister’s former press secretary Allegra Stratton in a Westminster briefing with journalists on March 8.

“Conservative Party funds are not being used to pay for any refurbishment of the Downing Street estate,” she had said.

But asked about suggestions to the contrary on Tuesday, Mr Johnson’s spokesman said: “I’ve seen the reports and the speculation on that, I’m not going to jump ahead of any potential declarations that need to be made.”

Mr Case, the head of the Civil Service, has been tasked with reviewing the refurbishment of the flat in No 11.

In a letter to the Cabinet Secretary, Ms Rayner said: “As a special adviser, Allegra Stratton is bound by the Civil Service Code, which sets out standards of integrity and honesty required from public officials.

“Therefore, I would urge you to build into your review an investigation into whether the former press secretary knowingly misled journalists and the public, or was misled herself by senior members of the Government who seem intent on a cover-up.”

Ms Stratton, who moved roles this month after No 10 scrapped plans to hold televised press briefings fronted by the former journalist, is yet to respond.

Shadow health secretary Jonathan Ashworth called for a “full and frank” explanation from the Prime Minister.

“We really need to know who’s given the loan, who’s given the money, because we need to know who the Prime Minister, who Boris Johnson, is beholden to,” the Labour MP told BBC Breakfast.

“To be honest he lied yesterday – that’s not good enough.”

Downing Street was moved to issue a further defence of Mr Johnson later in the day, but it also stopped short of ruling out a loan from CCHQ.

“Any costs of wider refurbishment this year beyond those provided for by the annual allowance have been met by the Prime Minister personally. Conservative Party funds are not being used for this,” a spokeswoman said in a statement.

Labour has said that the “stench” surrounding the issue “will only grow” unless Mr Johnson publishes the long-delayed list of ministers’ interests.

Mr Johnson’s spokesman said that list, last published in July, would not be updated until after No 10 appoints a new independent adviser on ministerial standards.

Sir Alex Allan resigned from the role in November in response to Mr Johnson standing by Home Secretary Priti Patel despite an investigation finding her conduct “amounted to behaviour that can be described as bullying”.

“The declaration of interests that will be made available once we’ve appointed the replacement for Alex Allan, that work is in train,” the spokesman said.

“One of the first things that person will then do is then look at the ministerial interests and then make sure they can be published in the normal manner.”

An update of the separate register of MPs’ financial interests on Tuesday showed no sign of a loan to Mr Johnson, with his only addition a £2,397 payment for book royalties.

Prime ministers get a budget of up to £30,000 per year to renovate their Downing Street residency, but newspaper reports have suggested Mr Johnson has spent up to £200,000.

Last week the Daily Mail published details of an email from Tory peer Lord Brownlow in which he said he was making a £58,000 donation to the party “to cover the payments the party has already made on behalf of the soon-to-be-formed ‘Downing Street Trust’”.

Labour has called for a full investigation by the Electoral Commission.