DAVID Cameron has launched another stinging attack on Boris Johnson, claiming the Prime Minister "didn't believe" in Brexit and only backed the Leave campaign to further his political career.

The former Conservative premier said Mr Johnson privately claimed there could be a "fresh renegotiation, followed by a second referendum," a move the PM insists he adamantly opposes.

In further extracts from his long-awaited memoir, Mr Cameron also launched another withering broadside against his onetime friend and colleague Michael Gove, branding the Cabinet Office Minister, a "foam-flecked Faragist".

And he accused the leaders of the Leave campaign of declaring "open warfare" on him, accusing them of "lying" to the public to win the 2016 referendum.

Mr Cameron wrote that the PM 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".

He claimed: "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 ex-PM let rip, declaring: "One quality shone through: disloyalty. Disloyalty to me and, later, disloyalty to Boris."

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

Mr Cameron went on: "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."

Mr Cameron said attacks by another leading Leaver Priti Patel, the Home Secretary, on his Government's immigration record "shocked me most" but he did not want to fire her and create a "Brexit martyr".

He also described another leading Leaver Dominic Cummings, who is now Mr Johnson’s de facto chief of staff, as being part of a "cauldron of toxicity" with Nigel Farage.

Meanwhile in further extracts from his memoirs, Mr Cameron opened up about the death of his eldest child, Ivan, saying how it made him feel "as if the world stopped turning".

He explained how he was "bursting with pride" on April 8, 2002 when his wife Samantha gave birth to the couple's first child.

Ivan was small but seemed healthy, though he was born by emergency caesarean section.

The former PM in his book, serialised in The Sunday Times, noticed how Ivan soon began to lose weight, was not feeding properly and was having seizures.

His son was diagnosed with Ohtahara syndrome, named after the Japanese physician who first observed it.

Mr Cameron wrote that the cause was unknown, the treatment options were uncertain and there was no cure.

"He could have 20 or 30 [seizures] in a day, lasting for minutes, or sometimes hours, his small frame racked with spasms and what looked like searing pain. By the end, his clothes would be drenched in sweat and his poor little body exhausted."

After years of medical difficulties and round-the-clock care, Ivan died at St Mary's Hospital in London on February 25, 2009, aged six.

"Nothing, absolutely nothing, can prepare you for the reality of losing your darling boy in this way. It was as if the world stopped turning," admitted Mr Cameron.

As then Leader of the Opposition, he was due at the House of Commons for Prime Minister's questions the next morning, but Gordon Brown, whose daughter, Jennifer Jane, had died a few days after she was born, adjourned the house for the day.

Mr Brown's "real warmth and humanity meant a lot to us," said the former party leader.

The Camerons had three more children after Ivan, daughters Nancy and Florence and son Arthur Elwen.