Boris Johnson has said any donations linked to the refurbishment of his Downing Street flat will be declared “in due course”.
The prime minister is under pressure to explain how works on the official residence were paid for, following claims from his former top adviser.
Dominic Cummings has alleged the PM once planned to have donors “secretly pay” for the revamp.
The defence secretary has said Mr Johnson “personally paid the bill”.
Speaking earlier, Ben Wallace added that Mr Johnson had covered the costs “from his own money” and complied with the rules “at all times”.
Labour has called on the Electoral Commission, which regulates political donations in the UK, to launch a formal investigation.
The watchdog has said it is talking to the Conservative Party about whether the spending on the flat falls within its remit.
The claims about the flat are contained in a blog posted by Mr Cummings on Friday, his first since leaving his role in No 10. In the blog he also:
Asked on Monday whether he had ever discussed using donations to pay for refurbishments, Mr Johnson replied: “If there’s anything to be said about that, any declaration to be made, that will of course be made in due course.”
The UK’s most senior civil servant, Cabinet Secretary Simon Case, is facing questions from MPs about Mr Cummings’s allegations.
Appearing before a Commons committee this afternoon Mr Case said the inquiry into the leak of plans for a second lockdown is “ongoing”.
Downing Street says the prime minister has “never interfered in a government leak inquiry”.
Like several of his recent predecessors, the PM is living in the flat above No 11 Downing Street, which is larger than the one above No 10.
Asked whether a loan had initially covered the refurbishment costs, Mr Wallace told BBC Breakfast: “The prime minister paid the money, from his own money”.
He said this came “on top of” public money from the annual £30,000 taxpayer grant available to all prime ministers for the upkeep of their accommodation.
In a written statement on Friday, the government said no money from this grant was spent in the 2019/20 financial year. Figures for this year are expected to be published in the summer.
“At all times the prime minister has complied with the rules. He’s paid for it out of his own money, ” he said.
Mr Wallace also dismissed as “nonsense” a newspaper report that Mr Johnson said he would rather see “bodies piled high in their thousands” than order a third national lockdown.
The Daily Mail quoted sources saying the remark came after the PM reluctantly imposed a lockdown in England in November. Downing Street has strongly denied he made the comment.
Asked about the claims, Mr Wallace said: “I’ve known the prime minister for many years, that is not the prime minister I know. That is just nonsense.”
Speaking to reporters on Monday, Labour leader Sir Keir Starmer urged a “full and transparent investigation” into the allegations about the Downing Street flat, arguing they risked undermining trust in government.
“It’s all very well the prime minister saying now ‘I paid for it’, the critical question was: what was the original arrangement – and why is it so complicated?”
“If there’s a straightforward answer, well give it. And if there isn’t, then there are very serious questions to be asked,” he added.
A No 10 spokesperson said: “At all times, the government and ministers have acted in accordance with the appropriate codes of conduct and electoral law.”
Donations and loans to political parties of more than £7,500 must be reported to the Electoral Commission.
The Conservative Party has previously said that all “reportable donations” are “correctly declared to the Electoral Commission, published by them and comply fully with the law”.
The party said “gifts and benefits received in a ministerial capacity” are declared in government transparency returns.