Mr Johnson will face Labour leader Sir Keir Starmer on Wednesday as the Prime Minister also faces pressure over allegedly saying he would rather see “bodies pile high” than impose a third shutdown.
Downing Street has refused to say whether Mr Johnson received an initial loan from the Conservative Party to cover renovations to his residence in No 11.
Labour has accused him of having “lied” over the funding, and accused senior members of the Government of a possible “cover-up”.
Transport Secretary Grant Shapps insisted a review into the controversy by Cabinet Secretary Simon Case will answer whether the Tory party gave Mr Johnson a loan, before the Prime Minister paid back the costs.
“I just don’t have the answer but the Cabinet Secretary will and it will be transparently produced in the annual report and the accounts of the Cabinet Office,” the Cabinet minister told Times Radio.
But Mr Shapps declined to say whether he would have approved the funding when he was party chairman, instead telling BBC Breakfast: “My side of things was the campaigning side of things, I didn’t get involved with the fundraising side of things.”
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.
A No 10 spokeswoman has said that the costs “have been met by the Prime Minister personally” and that party funds “are not being used for this”.
But Downing Street has refused to answer whether party funds were used in the past, as the Electoral Commission looks into the controversy.
It is likely Mr Johnson will also face questioning over whether he said he was prepared to let “bodies pile high” rather than order a third shutdown, an accusation he has branded as “total rubbish” and one which has been denied by No 10.
But after the Daily Mail first reported the remarks, the BBC and ITV were among those to carry reports with their own sources confirming he made the comment in October.
Downing Street officials have been less firm on a Times report that Mr Johnson separately told aides in September he would rather let coronavirus “rip” than impose a second lockdown.
The Prime Minister’s official spokesman said the reports “distort the actions” of Mr Johnson, but the defence did not amount to a denial.
The bombardment of allegations around the Prime Minister come as he is embroiled in a public row with Mr Cummings, who until last year was his senior adviser in No 10.
Mr Cummings hit out at his former boss in a blog post, saying he had fallen “below the standards of competence and integrity the country deserves” after No 10 sources – reportedly the Prime Minister himself – accused him of being behind a series of leaks.
Shadow health secretary Jonathan Ashworth called for a “full and frank” explanation from the Prime Minister over the funding of the renovations.
“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 has told BBC Breakfast.
“To be honest, he lied yesterday – that’s not good enough.”