Ministers have denied claims that Boris Johnson was prepared to let “bodies pile high” rather than order another coronavirus lockdown, as the fallout from Downing Street’s bitter briefing war continued.

Defence Secretary Ben Wallace said it was “not true” to suggest Mr Johnson made that comment, while Health Minister Nadine Dorries said it was an “outright lie”.

The remarks were reportedly made after the Prime Minister agreed to a second lockdown, and suggest Mr Johnson was prepared to face a mounting death toll rather than order a third set of tough restrictions, something he was eventually forced to do.

The decision on the second lockdown last autumn was leaked and is the subject of an inquiry to find the so-called “chatty rat” who tipped off the press.

The UK’s most senior civil servant is expected to indicate he has not cleared Mr Johnson’s former adviser Dominic Cummings over that leak, despite the ex-aide’s claims to the contrary.

Simon Case, the Cabinet Secretary, is expected to say his inquiry is still “live” when he appears before the Commons Public Administration and Constitutional Affairs Committee (PACA ) on Monday.

Mr Cummings has accused Mr Johnson of seeking to block the investigation after learning that a close friend of his fiancee, Carrie Symonds, had been implicated, a claim the Prime Minister denied.

In an incendiary blog post, Mr Cummings went on to say that Mr Case had told Mr Johnson that neither he nor the then No 10 director of communications, Lee Cain, was the culprit.

However officials familiar with the investigation said that it had neither “landed” on any one individual nor exonerated anyone.

The disclosure is likely to further anger Mr Cummings, who released his onslaught after he was accused by No 10 of a series of damaging leaks, including text message exchanges between Mr Johnson and the entrepreneur Sir James Dyson.

Ministers are now concerned at what he may say when he gives evidence to MPs investigating the Government’s response to the pandemic next month.

Mr Cummings is widely known to have been critical of Mr Johnson’s delay in launching a second lockdown in England when cases began rising last autumn, and there is speculation he will seek to blame him for the high death toll.

The Daily Mail carried the claim that, following the lockdown, the Prime Minister said he would rather see “bodies pile high in their thousands” than order a third one.

The paper did not give a source for the allegation, but ministers hit out at “gossip” spread by “unnamed advisers”.

Mr Wallace told Sky News: “We are getting into the sort of comedy chapter now of these gossip stories – unnamed sources, by unnamed advisers talking about unnamed events.

“None of this is serious. The Prime Minister has been utterly focused on delivering, alongside Cabinet colleagues, the response to Covid.”

Ms Dorries said it was “mendacious, vexatious, co-ordinated gossip” aimed at destabilising the Tory campaign ahead of the May 6 elections.

Meanwhile Labour will focus on another of Mr Cummings’ allegations as it attempts to force ministers to explain how Boris Johnson paid for the lavish refurbishment of his official Downing Street flat.

The opposition will ask Commons Speaker Sir Lindsay Hoyle to grant an urgent question requiring a minister to come to the House to respond to the charge that Mr Johnson plotted for Tory donors to secretly fund the work.

Labour deputy leader Angela Rayner said there was a “real stench” around the Government and she called for the Electoral Commission, which polices the party funding rules, to launch a full inquiry.

The commission, which first raised the issue with the Conservative Party more than a month ago, confirmed at the weekend it was still looking into whether any of the sums relating to the work on the flat should have been declared.

Mr Wallace said the Prime Minister paid for the renovations “out of his own pocket”.

“The Prime Minister has complied at all stages with the rules and we’ve been very clear on that,” he told BBC Radio 4’s Today.

“We have engaged with the Electoral Commission and we will continue to engage with that.”

Mr Case, meanwhile, is likely to face questions during his appearance before the PACAC, about another issue where Labour is hoping to make ground, what it describes as Tory “sleaze”, David Cameron’s lobbying on behalf of Greensill Capital.

MPs are expected to press him on the extent of the former prime minister’s activities on behalf of the failed finance company, following the disclosure that he used his contacts to directly approach Chancellor Rishi Sunak, Health Secretary Matt Hancock and the deputy governor of the Bank of England.

Earlier this month Mr Case ordered all senior civil servants to declare whether they had outside jobs, after it emerged that the former head of government procurement had taken a position with Greensill while still working in Whitehall.