Dominic Cummings at No 10 with his book on Chinese spies

When Boris Johnson first approached Dominic Cummings during the Conservative leadership election, the former Vote Leave mastermind played hard to get.

“He said he needed to be in charge of everything,” one source privy to the discussions at the time said.

They were, he joked, his “terrorist demands” of a prime minister-in-waiting who badly needed a heavyweight enforcer. It took several meetings before the men could agree terms.

But despite the promise since Mr Johnson’s emphatic election victory two months ago, ministers have ruefully noted that Mr Cummings has been on the losing side of the most significant domestic arguments that have landed on the prime minister’s desk.

He vehemently opposed giving the go-ahead to the HS2 rail network that he described as a “disaster