David Cameron, the former British prime minister, has launched a scathing attack on the United Kingdom's current leader, claiming in extracts from his memoir published in the Sunday Times that Boris Johnson is not committed to the nation exiting the European Union but is merely championing the cause for political expediency.

Cameron, who led the UK for six years until 2016, says in For the Record that Johnson did not believe in Brexit during the 2016 referendum campaign but that he became a prominent member of the Leave camp "because it would help his political career".

Cameron, who triggered the referendum following pressure from within his Conservative Party, campaigned for the UK to remain a member of the EU.

He said, with the benefit of hindsight, he can see that it was easier to rouse voters by promising change than it was by promising the status quo, a bandwagon, he says, that both Johnson and senior minister Michael Gove soon joined.

"Whichever senior Tory (Conservative Party) politician took the lead on the Brexit side – so loaded with images of patriotism, independence and romance – would become the darling of the party," he wrote. "He (Johnson) didn't want to risk allowing someone else with a high profile – Michael Gove in particular – to win that crown."

Cameron said both Johnson and Gove behaved "appallingly" during the campaign ahead of the referendum, which was narrowly won by the side wanting the UK to leave the EU after it made claims that have since been debunked; such as the exit meaning an extra 350 million pounds ($436 million) a week for the National Health Service.

"The conclusion I am left with is that (Boris Johnson) risked an outcome he didn't believe in because it would help his political career," Cameron wrote.

He also criticized the employment minister at the time of the referendum, Priti Patel, who is now home secretary, saying she "used every announcement, interview and speech to hammer the government on immigration, even though she was part of that government".

Cameron resigned immediately after the referendum result was revealed and has said little in the following three years.

The BBC said neither Johnson, Gove, or Patel chose to respond to Cameron's claims.

Johnson, meanwhile,was set to meet European Commission President Jean-Claude Juncker in Luxembourg on Monday to discuss whether a new and improved Brexit divorce deal can be found.

Johnson told the Mail on Sunday newspaper he remains hopeful he can get a better deal before a key EU summit on Oct 17.

He insisted there had been movement in the negotiating positions of Germany, France, and the Republic of Ireland.

"I think that we will get there," he said.

The Financial Times said Johnson hopes to secure a deal with the EU at the summit and then get it through Parliament in a 10-day window that will include late-night and weekend sessions.

The paper said EU diplomats were also more optimistic. Following talks on Friday in Brussels some said more progress had been made than in previous meetings.