The briefing given to Express.co.uk from a Downing Street source comes as the race to replace Mr Johnson has turned nasty with a series of under-the-radar attacks on the leading candidates. Last night sources revealed that Chancellor Nadhim Zahawi, who replaced Mr Sunak in the Treasury just a few days ago, is under investigation for his tax affairs by his own department in HMRC. Added to that a dossier with a series of allegations about Mr Sunak is being shared with undecided Tory MPs.
A source in Downing Street still loyal to the Prime Minister who was forced to say he will step down on Thursday has insisted that Mr Sunak is in hock with the controversial Mr Cummings who is accused of turning Downing Street “toxic” when he worked for Mr Johnson as chief of staff.
He then was at the centre of efforts to force Mr Johnson out Tweeting a series of allegations about Partygate and other issues after he was sacked in December.
A senior Number 10 source told Express.co.uk that former education secretary Gavin Williamson, who was Theresa May’s controversial chief whip, is also at the centre of plans to make sure their man Mr Sunak becomes Prime Minister.
The source said: “Williamson and Cummings have been running Rishi and his campaign.
“Williamson has been involved since winter. Cummings has been involved since day 1.
“Williamson master plan is to ensure a Rishi v Hunt final. Hunt is the only candidate Rishi beats.”
An MP, involved in one of the rival campaigns but still close to Mr Johnson, added: “Williamson will move numbers around to get Hunt into the final 2. Once in, Cummings will run the show again.”
A spokeswoman from the Rishi Sunak campaign angrily denied the allegations as an attempt to smear Mr Sunak.
She said: “”Mr Cummings has nothing to do with the campaign. He and Rishi have not spoken since he left no 10 almost two years ago.”
A senior source in the Sunak campaign added: “It’s all b******s to be very clear!”
Mr Williamson did a similar operation when he was helping Mr Johnson win in 2019.
As a former Chief Whip he is good at organising MPs and ensuring the numbers are right in votes.
He was credited with switching Boris Johnson supporters to Jeremy Hunt at the last minute to stop Michael Gove get into the final two with members.
At the time the Johnson operation had identified Gove as their biggest threat even though he as dealing with revelations that he had used cocaine at a party.
The briefings against candidates are aimed at knocking out leadership bids while they scramble to win enough support from MPs.
And it is understood that Mr Sunak is a prime target because of his resignation last week which has led to speculation that the briefings against Mr Sunak from Downing Street are partly “Boris’ revenge.”
One source claimed: “The Prime Minister took that resignation very personally becase he had stood by Rishi [Sunak] through all his problems.”
One former Vote Leave MP said that “it was hard to remember a time when Mr Sunak actually campaigned for Brexit.”
However, the allegation has been dismissed as being “ridiulous” by one Brexiteer MP who pointed out that the Richmond MP did turn down an offer from David Cameron to join the Remain team and delayed a likely ministerial promotion.
The dossier being passed around focuses on his record as Chancellor.
It claims he “enabled Boris Johnson’s reckless overspending and increased UK taxes to the highest level since [Labour Prime Minister] Clement Atlee.”
Italso highlights that like Mr Johnson he was fined over Partygate and points out that he had a Green Card to work in the USA among other allegations.
A source close to the Sunak campaign said: “Rishi must be doing well if they want to throw all this s*** at him.
“They obviously think he is the man to beat.”