Boris Johnson will face MPs in the Commons as he battles accusations from Labour that he lied over who paid for renovations to his Downing Street flat.
The PM will appear at Prime Minister’s Questions for the first time since his ex-adviser accused him of planning for donors to “secretly pay” for the work.
A No 10 spokesman has refused to say whether Mr Johnson initially received a loan to cover the costs.
Labour have demanded a detailed explanation from the prime minister.
While it is not against the rules to receive donations, politicians must declare them so the public can see who has given them money and whether it has had any influence on their decisions.
Mr Johnson has told reporters any relevant donations would be declared “in due course”.
And his spokesman said the costs “have been met by the prime minister personally”.
But No 10 has not yet made clear exactly how the works were paid for in the first place and declined to say whether the prime minister received a loan from the Conservative Party.
Mr Johnson is also likely to be asked at Prime Minister’s Questions about accusations he said he would rather see “bodies pile high” than approve a third lockdown.
The comment was first reported in the Daily Mail – but later, the BBC and ITV separately reported sources confirming Mr Johnson did make the remarks.
However, No 10 strongly denied he said the phrase, and the PM described the reports as “total rubbish”.
A Downing Street spokesman did not deny that Mr Johnson said he would rather let coronavirus “rip” than impose tighter restrictions.
Questions over the prime minister’s flat were triggered when his former aide Dominic Cummings detailed his own take on Mr Johnson’s plans in a blog published on his website.
Like many previous prime ministers, Mr Johnson chose to live in the flat above No 11 Downing Street rather than the smaller apartment in No 10.
Prime ministers are given £30,000 to spend on renovating their new home. However, it has been reported that Mr Johnson’s changes cost up to £200,000.
Speaking to BBC Breakfast on Tuesday, Labour’s shadow health secretary Jonathan Ashworth said any loans or donations to cover the costs “should have been declared by now”.
“We really need to know who’s given the loan, who’s given the money, because we need to know who the prime minister…is beholden to,” he said.
“To be honest he lied yesterday – that’s not good enough.”
Asked about the possible donations, Transport Secretary Grant Shapps said “there will be a Cabinet Office report when they put out their annual accounts and everyone will be able to see exactly what happened”.
Mr Johnson’s spokesman said the prime minister had “acted in accordance with the appropriate codes of conduct and electoral law”.
On Monday, Cabinet Secretary Mr Case – the UK’s most senior civil servant – told MPs the prime minister had asked him to review how the refurbishment of the No 11 flat was funded.
Sky News and the Guardian have reported that last July former Labour Chancellor Alistair Darling was asked by government officials about whether he would sit on a trust to handle a Downing Street refurbishment.
He reportedly rejected the offer on the grounds that it risked giving donors influence and that the state should be responsible for the maintenance of government buildings.