Boris Johnson was perched on a sofa in the basement of his home in Islington, north London, with no socks on, when he began to realise that he might be the next prime minister.

It was 8.15am on Friday and the former mayor of London was working on a speech calling for Tory unity when David Cameron walked to the podium outside 10 Downing Street and announced, voice breaking with emotion, that he was resigning after six years in office and 414 days after he won a historic majority.

Johnson had no idea his fellow Old Etonian and sparring partner for two decades was about to quit. Those present say Johnson was “pretty emotional” at what had transpired in the hours before when his band