Number 10 fears Dominic Cummings bombshell dossier

Downing Street insiders are increasingly fearful that a devastating "treasure trove" of internal memos and emails from Dominic Cummings will paint the Government in the worst possible light at the height of the Covid crisis.

Mr Cummings, Boris Johnson's former chief adviser, is appearing before a joint committee of MPs investigating Whitehall's response to the virus crisis next month.

Jeremy Hunt, the chairman of one of the committees that will question him, on Saturday night confirmed to The Telegraph that MPs would publish whatever the former Downing Street aide gave them as long as it did not put national security at risk, as long as the MPs on the committee agree.

Mr Hunt said: "We will publish whatever he gives us – we would have to check if it passes any tests."

Downing Street insiders have no idea the extent of the material Mr Cummings claims to have and say they are "terrified" about further revelations.

One Westminster insider said there is extreme nervousness about an apparent "treasure trove" of embarrassing documents that Mr Cummings – who quit 10 Downing Street last November, carrying a cupboard box – might want to get published.

The insider said: "Apparently he has got loads of stuff. No one has a real clue about what documents, emails and texts he actually has. They don't know how much he has, nor what he has.

"The fear is that Boris [Johnson] had to be dragged to the second lockdown [in November] and I think they are worried it is going to make everyone who isn't him look very good because him and Rishi [Sunak] were the only two who did not want to do the lockdown."

A second Government source added that, in Whitehall meetings, Mr Cummings "used to scribble a lot in that book. I don't know what he has got, what he has not got".

The news comes as Britain's top civil servant faces being dragged into the battle between Boris Johnson and his former ally when he is questioned by MPs at the Public Administration and Constitutional Affairs select committee on Monday.

Sources on the committee said that Simon Case, the Cabinet Secretary, will be quizzed about his recollection of a conversation with Mr Cummings in which he suggested that Henry Newman, a friend of Carrie Symonds, was the source of "chatty rat" leaks, including one about the timing of the second lockdown.

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In a 1,000-word blog post, Mr Cummings claimed Mr Case had told him that "all the evidence definitely leads to Henry Newman and others in that office, I'm just trying to get the communications data to prove it".

He alleged that the Prime Minister then personally asked him if it was possible to stop the leak inquiry because it would cause him "very serious problems" with his fiancée.

Mr Cummings claimed Mr Johnson said that if Mr Case discovered the leaker was Mr Newman then he would have to fire him and this would cause some "very serious problems with Carrie as they're best friends".

MPs on the committee will also ask him about why – according to Mr Cummings – Mr Johnson had asked donors to renovate his flat in Downing Street, before Number 10 said on Friday that the Prime Minister will pay for the work after all.

On Saturday night Labour's shadow Cabinet Office minister, Rachel Reeves, wrote to Mr Johnson calling for a "full investigation" into the sums spent on the flat.

Mr Cummings made clear in an explosive blog last week that he would answer questions about Number 10's handling of the pandemic "for as long as the MPs want" when he gives evidence to MPs on the Health and Science committees on May 26.

In his only public remarks since publishing the blog, he posted an apparently ominous tweet referencing the debate about closing borders during the pandemic which read:

Westminster insiders are mystified why Mr Johnson chose to pick this fight with someone who could cause him so much political damage. Some Tories believe left-leaning civil servants have been responsible for some of the leaks, particularly those linked to David Cameron and the failed finance firm Greensill.

One insider said: "People in Downing Street don't really understand why Boris has kicked this, put his finger inside the hornets nest."

One senior Conservative MP said: "It is a complete mess. I am afraid it is factionalism of the worst kind combined with the personal situation of the Prime Minister's other half. It is really unacceptable and the only person who can sort it out is the Prime Minister. It is tawdry."

Another very senior Tory MP added: "Don't ask me what is going on in Downing Street, because I just don't know."

There were concerns that the rows could damage the Conservatives in a Super Thursday of local, mayoral and regional assembly elections next month.

One senior Cabinet minister added: "Everyone just needs to calm down and shut up on both sides. Some people who think attacking Dominic Cummings is supporting the Prime Minister – it isn't. Let's live and let live on all sides.

"We all – both the Prime Minister and Dominic – share many beliefs in terms of policy and the direction we want to take the country. We are all on the same side here. The only person who wins after this pathetic slagging match is Keir Starmer."

In a rare public intervention, Mark Spencer, the Government's chief whip, appealed for the different factions to stop "fighting previous battles".

He told The Telegraph: "Communities up and down the country are dependent on the Conservative Party representing them and improving their lives, and that is what we should all be concentrating on – not fighting previous battles.”

Mr Johnson is increasingly isolated in 10 Downing Street following the imminent departure of his chief strategic adviser Lord Lister-Udny. Politicshome reported on Saturday that the peer was a director of a firm that was aiming to build a "Hong Kong" in Libya, while serving as a non-executive director at the Foreign Office.

Number 10 said he had "declared any relevant interests in accordance with the appropriate codes of conduct".

That came as The Telegraph disclosed the preferred candidate to be the Prime Minister's new adviser on ministerial interests – who was due to be unveiled last week – might not now take up the position following the chaos in Downing Street.

There were calls for Mr Johnson to appoint MPs who know him well from before he was PM, such as Conor Burns, Jake Berry and Nigel Adams, to senior Downing Street roles to stop damaging rows with Mr Cummings from breaking out.

One insider said that those inside Number 10 were "s******* themselves" ahead of potentially damaging revelations from Mr Cummings.

Several Government sources made clear on Saturday that the so-called "chatty rat" investigation into leaks from 10 Downing Street was still ongoing.

Friends of Mr Newman mounted a rearguard effort to shore up his position after he was named as a possible source of the leak. They pointed out that he did not even attend the relevant meeting from which details were leaked because he was not working in Number 10 at the time.

A senior official said: "The investigation is still live. It would be wrong to think we have landed on any one individual or, for that matter, completely exonerated anyone."

A Cabinet Office spokesman said: "We do not comment on leak investigations. Senior appointments at Number 10 go through rigorous checks."