The Mail on Sunday that the former PM was 'bitter', while another questioned the logic of his Brexit remarks.

They said: 'I don't understand why he has done it. He will always be hated by Remainers and, by apologising for Brexit, he will never get credit for having being the person who enabled it.'

The Mail on Sunday can reveal that Mr Cameron has personally assured some of the 21 former Tory MPs kicked out after voting against the new Prime Minister that he would help them try to keep their seats in the Commons, even if it means pounding the streets of their constituencies with them against a Tory candidate.

The incendiary promise – which would see a former Prime Minister actively working against his own party – comes amida furious backlash over the publication of Mr Cameron's explosive memoirs (pictured)

Mr Johnson has faced growing calls from within his own Cabinet and on the Tory benches to reinstate the rebels, including former Ministers Ken Clarke, Philip Hammond and Greg Clark.

A rebel source said: 'David reached out to lots of us and even said he would come and campaign if we stood as independents. He was very open about it on the phone.'

The revelation risks further souring relations between Mr Cameron and Mr Johnson, after Downing Street ordered Ministers not to attack the former PM in a bid to 'rise above' the memoirs row.

Despite insisting that he wanted the Prime Minister to succeed, Mr Cameron said Mr Johnson had behave 'appallingly' during the Brexit vote, and claimed his