Cabinet minister Liz Truss has insisted Boris Johnson "fully complied" with the rules over renovating his official Downing Street flat, dismissing Dominic Cummings’ claims to the contrary as "tittle-tattle".
Speaking to Sky News' Sophy Ridge on Sunday, the international trade secretary said the prime minister had personally met the costs of the renovation work.
But she also repeatedly refused to say whether he ever received the money to pay for it from a Tory donor or from the party itself.
It comes as the government faces increasing pressure to answer questions over the issue after Johnson's former top aide made a series of bombshell claims in a statement on Friday.
Cummings alleged that Johnson initially tried to have a party donor pay for the flat renovation and that the government in general lacked integrity.
He also claimed Johnson sought to block an inquiry into how news of the second national lockdown in November was leaked to the press after a friend of his fiancee was implicated.
But Truss told Sophy Ridge on Sunday: "I have been assured that the rules have been fully complied with and I know that he has met the costs of the flat refurbishment.
"I absolutely believe and trust that the prime minister has done that. What people want to know is that in line with the rules the prime minister has met the cost of this refurbishment. That has happened. All the costs will be declared in line with the rules.
"That, as far as I am concerned, completely answers that question."
Truss also said the inquiry into the so-called "chatty rat" leak of plans for the second lockdown in England was ongoing.
Watch: Cummings denies being source of leaked PM's texts with Dyson
She dismissed Cummings' claims that Johnson sought to block the probe, saying: "This is tittle-tattle that is being promoted and I don't think it really addresses the key issues that people in Britain care about.
"The prime minister, who I work very closely with, has consistently through this crisis acted in the best interests of the country.
"These noises off are simply not helpful, they are not contributing to a positive future and they don't reflect what is actually going on in Downing Street."
However, her comments came as Labour’s deputy leader Angela Rayner reiterated the party’s calls for the government to answer questions around its conduct.
She told BBC One's The Andrew Marr Show: "There is serious questions now that the Conservatives need to answer around how they've dealt with their mates who have been fast-tracked through a VIP list to get contracts."
On the Downing Street flat, she added: "The Electoral Commission should be looking into it absolutely and doing a full investigation, especially as you've got a former senior adviser to the prime minister suggesting that not only was it unethical but he believes it could be illegal as well.
"These are serious allegations and we also think the prime minister should come to the House of Commons on Monday and should declare the ministers' register of interests, which is eight months in delay, we've not seen that. Why are they hiding the fact that ministers have to declare these donations and they've not done that?
"That's serious and the list of the VIPs who got contracts who seem to be mates of Tories or Tory donors, this is a real stench around what government is about."
Meanwhile, Labour's Jess Phillips also called for a "root and branch" independent inquiry into the use of taxpayers' money under Johnson's government.
The shadow minister for domestic violence and safeguarding told Sophy Ridge on Sunday: "The truth of the matter is we don't know the truth and we've got scrapping between two very powerful men who seem more interested in who's lying about what and who's leaking what than the substantive of the issue.
"That is whether contracts get given out by text messages, whether tax breaks get given out by text messages or whether the prime minister uses his pals to get money to have his flat done up.
"Whether I back Dominic Cummings' view or Boris Johnson's view, what we need is a proper independent inquiry where it isn't about two boys fighting and is about taxpayers in our country."
Phillips indicated Labour would be seeking an urgent question in parliament on the issue, adding: "Integrity really, really matters."
Watch: Johnson and Cummings are 'two boys fighting'