The UK’s most senior civil servant will be questioned by a committee of MPs later on lobbying rules and claims made by ex-No 10 adviser Dominic Cummings.
Cabinet Secretary Simon Case is expected to be asked about allegations the PM considered halting a leak inquiry in case it implicated his fiancee’s friend.
No 10 says this is “absolutely false”.
Mr Case is expected to say the inquiry into the leak of plans for a second lockdown last autumn is ongoing.
He is appearing before the Commons Public Administration and Constitutional Affairs Committee.
Meanwhile, Labour is trying to maintain pressure over the funding of refurbishments to the prime minister’s Downing Street flat, saying questions remain over how the work was paid for.
Its lawyers have written to the Electoral Commission, which examines party funding rules, asking for a full inquiry, saying it is “incontrovertibly in the public interest”.
Mr Cummings, who left his adviser role in November, launched a blistering attack on his former boss via his blog on Friday, claiming the PM had considered asking Tory donors for funds for his Downing Street flat revamp. No 10 says the cost was met by Boris Johnson.
In his blog, Mr Cummings denied being the source of a leak last year ahead of the second Covid lockdown in November. An investigation was launched after briefings to the press led Mr Johnson to announce England’s lockdown earlier than planned.
Mr Cummings said an inquiry at the time found that neither he nor the then-Downing Street director of communications, Lee Cain, had been responsible.
He added that the events around that inquiry “contributed to [his] decision to stick to [his] plan to leave No 10 by 18 December”, which he says were “communicated to the prime minister in July”.
The former adviser also claimed Mr Johnson had considered stopping the inquiry.
He wrote that he recalled a meeting between Mr Johnson and the cabinet secretary at the time, after an inquiry had been launched, at which the cabinet secretary allegedly said “all the evidence definitely leads to Henry Newman and others in that office”.
At the time, Mr Newman was a special adviser at the Cabinet Office. He took up a role in Downing Street earlier this year.
Mr Cummings claimed that, in a conversation he had with the PM afterwards, Boris Johnson said: “If Newman is confirmed as the leaker then I will have to fire him, and this will cause me very serious problems with Carrie [Symonds – the PM’s fiancee] as they’re best friends… [pause] perhaps we could get the cabinet secretary to stop the leak inquiry?”
In response to Mr Cummings’ claims, a Downing Street statement said: “The prime minister has never interfered in a government leak inquiry.”
And a senior government official said: “The allegations against Henry Newman are entirely false. He wouldn’t be working in Downing Street if he was suspected of leaking information.”
‘From his own pocket’
Mr Cummings also claimed he advised the PM his flat renovation plans were “unethical, foolish, possibly illegal and almost certainly broke the rules on proper disclosure of political donations if conducted in the way he intended”.
Trade Secretary Liz Truss, told the BBC’s Andrew Marr Show on Sunday that Mr Johnson covered the renovation costs for his Downing Street flat “from his own pocket”.
But she did not answer repeated questions on whether a Tory party donor initially provided the money to him.
Mr Johnson lives in the flat above 11 Downing Street with Ms Symonds – a move echoing a number of his predecessors as it is bigger than the accommodation above No 10.
In March, Downing Street dismissed as “speculation” suggestions that refurbishments on the flat last year would be paid for by Tory donors through a charity set up for this purpose, amid reports that the costs had spiralled out of control.
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.”
And Cabinet Office Minister Lord True told the House of Lords on Friday that “any costs of wider refurbishment in this year have been met by the prime minister personally”.
Donations and loans to political parties of more than £7,500 must be reported to the Electoral Commission, which said it was having “discussions with the Conservative Party”, but had not yet launched an investigation.
The controversy also comes amid an ongoing row over lobbying in Westminster, after revelations former prime minister David Cameron had texted ministers about the financial firm he was working for and businessman Sir James Dyson had directly contacted Mr Johnson over tax issues when working on ventilators during the pandemic.
Meanwhile, Labour is also calling for the publication of all contacts and links between ministers and firms awarded government contracts during the Covid crisis.
The government said “due diligence is carried out on every contract”.