Mr Johnson’s future in the Cabinet has come under question after he set out a detailed vision of Britain’s post-Brexit future that has been viewed as a challenge to Theresa May’s leadership.
The Foreign Secretary publicly declared he is “all behind Theresa for a glorious Brexit” after the 4,000-word assessment of Brexit fuelled speculation about his ambitions.
Mr Johnson revived the widely-criticised claim quitting the EU could boost NHS coffers by up to £350 million a week and warned against paying for access to European markets in the future.
But the in-depth article on life after March 2019 was released just six days before the Prime Minister sets out her Brexit blueprint in a speech in Florence.
It has prompted claims in the Mail on Sunday that allies of the PM believed the move was “hostile” and “attention seeking”.
A senior minister who backed Remain told the Sunday Telegraph, meanwhile, Mr Johnson “needs to go and do something else” if he “can’t settle” into his role as foreign secretary while a former minister said he was “sailing within an inch of being thrown out of the Government”.
Sir Craig Oliver, former director of communications at Downing Street for David Cameron, said even if the genuine intention was to support the Prime Minister, it was obvious it would be seen in Westminster as a “direct challenge”.
But as the furore raged, Mr Johnson insisted in a tweet he was “looking forward to PM’s Florence speech”.
“All behind Theresa for a glorious Brexit,” he added.
In his plan for Brexit, Mr Johnson suggested continued membership of the single market and customs union would make a “complete mockery” of the referendum result.
Writing for the Daily Telegraph, he said the Government should “seize the opportunity” of Brexit to reform the UK tax system to boost investment, he suggested.
Rules restricting foreign buyers from snapping up property could be imposed once Britain leaves the EU but the UK should not slam the door on immigration, he wrote.