A former soldier and pro-Indian and anti-China in his views, Tom Tugendhat, chair of the Commons foreign affairs committee, is already in the running. Some rate the chances of foreign secretary Liz Truss very highly.

Incidentally, one important appointment that Boris made when Brandon Lewis resigned from the cabinet as Northern Ireland secretary was to replace him with an Indian, Shailesh Vara. The latter, who came from Uganda as a child and is MP for North West Cambridgeshire, was minister of state at the Northern Ireland Office under Theresa May but quit after five months in 2018 because he disagreed with her Brexit policies. Boris did not offer him a job until earlier this week.

There now appears to be bad blood between Boris and Sunak, who has been critical of the Prime Minister’s economic policies and especially his desire to spend more when the chancellor wanted to keep control of public expenditure.

A Downing Street source said Boris had backed his chancellor to the hilt and accused Sunak of having a short memory.

The BBC commented: “Prime Ministers typically don’t get involved in leadership contests for their successor. But Boris is not a typical leader. He may stay above the fray. But it’s safe to say Rishi Sunak won’t be getting his endorsement.”

The number of candidates will be reduced to two by Tory MPs in a succession of votes. The final two will then be put to the Tory membership at large across the country before the new prime minister moves into 10, Downing Street in September.

If Sunak makes the final two, he may well not be rewarded for bringing Boris down. There is a Macbethean saying in British politics: “He who wields the knife never wears the crown.”

Sunak’s video was filmed over two days by Cass Horowitz, the social media expert who created the chancellor’s personal brand and the son of the author Anthony Horowitz (who has written a new Sherlock Holmes book).

In the video, Sunak told the story which he recounted to Indian journalists on July 1. His grandmother had come from East Africa when his mother was only 15. In time his mother set up a pharmacy where the young Sunak helped out. His father had been a GP in the NHS. There were accompanying black and white photographs.

But The Times said Sunak had avoided “any details of his education at Winchester, Oxford and Stanford, nor his hedge fund career that made him rich, nor his marriage to an IT heiress that made him far richer”.

On Saturday, Conservative MP Liam Fox described Sunak as “an outstanding individual” who was best placed to deal with the economic challenges facing the country. “What I want to see is somebody who’s actually got a plan to see the spending of the government-controlled over time.”

Another Sunak supporter, Mark Spencer, a former chief whip and now leader of the Commons, said the former chancellor was responsible for saving “millions of jobs", adding “that’s a fantastic track record”.

But the knives were out for Sunak as well. Jacob Rees-Mogg, the Brexit opportunities minister, dismissed him as a “socialist chancellor”. One supporter of Truss said: “It’s absolutely true that Rishi put up taxes while many in government were saying, ‘Lower them’.”