Former British prime minister David Cameron has said Boris Johnson "didn't believe" in Brexit and only backed the Leave campaign to further his career.

Mr Cameron, who called the Brexit referendum, said Mr Johnson privately claimed there could be a "fresh renegotiation, followed by a second referendum" - which the current prime minister now says he opposes.

In extracts of his long-awaited memoir serialised in the Sunday Times, Mr Cameron also labelled Brexiteer Michael Gove, who was once a close friend, a "foam-flecked Faragist".

And he accused the leaders of the Leave campaign of declaring "open warfare" on him - and claimed they were guilty of "lying" to the public to win the 2016 referendum.

Mr Cameron wrote that Mr Johnspm wanted to become the "darling of the party" and "didn't want to risk allowing someone else with a high profile - Michael Gove in particular - to win that crown".

"The conclusion I am left with is that he risked an outcome he didn't believe in because it would help his political career."

On Mr Gove, the former PM said: "One quality shone through: disloyalty. Disloyalty to me and, later, disloyalty to Boris."

And he said Mr Gove's claim that the public were tired of experts made him "an ambassador for the truth-twisting age of populism".

"By the end, Boris and Michael seemed to me to be different people. Boris had backed something he didn't believe in.

"Michael had backed something he did perhaps believe in, but in the process had broken with his friends ... while taking up positions that were completely against his political identity.

"Both then behaved appallingly, attacking their own government, turning a blind eye to their side's unpleasant actions and becoming ambassadors for the expert-trashing, truth-twisting age of populism."