LONDON — David Cameron offered Boris Johnson a top-five Cabinet position in early 2016 in an effort to secure his support for the campaign to keep the UK in the European Union ahead of the Brexit referendum, according to revelations in a BBC documentary. The offer was made during a private tennis match between the two at the U.S. ambassador’s court next to Regent’s Park.

Cameron described the proposed role as one of the government’s most senior posts, such as defense secretary. “I didn’t say which job it was, I said: ‘Be in no doubt, defense is a top five job, for instance.’ I wanted him to understand that I valued his contribution, that he would be a major part of the government going forward,” Cameron said in the documentary.

Johnson said in the same program that Cameron told him: “Look, would you consider joining us on the remain campaign? It’d be much better if I’d love to have you in the Cabinet. You should have a top five job.” Johnson added he was unsure what the fifth top position would be, noting, “There’s prime minister, chancellor, home secretary, foreign secretary. That’s four. What is the fifth? A mystery.”

Cameron had invited Johnson to the tennis match specifically to discuss his stance on the upcoming EU referendum. Craig Oliver, who served as Cameron’s director of communications at the time, said Cameron returned from the encounter “feeling doubly good” because he had beaten Johnson at tennis and believed Johnson might join the remain campaign.

Despite the offer, Johnson announced in February 2016 that, “after a huge amount of heartache,” he would support the campaign for the UK to leave the EU. On the day of that announcement, Cameron pleaded with Johnson not to “link arms” with Nigel Farage and George Galloway in backing a British exit from the EU.

The revelations were featured in the first episode of a two-part BBC documentary titled 'A Very British Civil War,' scheduled to air on 8 June. Cameron also noted in the documentary that he could use the U.S. ambassador’s tennis court in what he called a “wonderful deal” for rest and recreation.