Sources close to the Foreign Secretary hit back at claims he was “on manoeuvres”, saying: “Boris’s article was about getting Brexit right and not about leadership.
“He thinks the Prime Minister is the right person to get this done.”
But his 4,000-word outpouring sparked criticism from Scottish Tory leader Ruth Davidson, with whom he clashed repeatedly during last year’s EU referendum campaign.
Questioning the timing of the piece, published yesterday, she tweeted: “On the day of a terror attack where Britons were maimed, just hours after the threat level is raised, our only thoughts should be on service.”
Will Tanner, a former adviser to Mrs May, called the timing astonishing, self-serving and disloyal.
Referring to Mr Johnson saying the UK would be £350million a week better off, Mr Tanner tweeted: “The real PM just raised threat level.
Meanwhile guy who wants to replace her issues a prelude to resignation, to save face over 350 million pounds. Hmm.”
Sir Craig Oliver, former director of communications at Downing Street for David Cameron, said even if the intention had been to support the PM, it was obvious that it would be seen in Westminster as a “direct challenge”.
He told LBC radio: “I think he is reminding people that he is there and is a force to be reckoned with.”
Liberal Democrat leader Sir Vince Cable called on Mrs May to “slap down” the former London mayor, dubbing him a “Poundland Donald Trump”, while a spokesman for Jeremy Corbyn said Boris has “laid bare the conflicts at the heart of Theresa May’s Government over Brexit and cut the ground from beneath her authority.”
Number 10 sources admitted Downing Street had been “blindsided” by the article, which they only found out about late on Friday afternoon.
One insider said: “We saw the copy a few hours before it was published but we were in the middle of a terrorist incident.
The PM was focused on the safety of the public following the explosion at Parsons Green.