THERESA May is facing calls to sack Foreign Secretary Boris Johnson, who was branded a “backseat driver” by a Cabinet colleague after setting out his own vision for Brexit just days before a major speech in which the Prime Minister is expected to offer compromise.

Johnson came under attack yesterday from Home Secretary Amber Rudd, who during the EU referendum campaign described him as “not the man you want driving you home”.

Rudd said she had been “too busy” dealing with the Parsons Green bomb attack in London to read a 4000-word article written by Johnson on his approach to Brexit – which he released at the time of the blast.

His article set out his opposition to paying the EU a large sum of money to settle the so-called “divorce bill” and restated his previous controversial claim that Brexit would lead to an extra £350 million a week to the NHS.

“I don’t want him managing the Brexit process,” she told told BBC1’s The Andrew Marr Show yesterday, saying the Prime Minister is “driving the car”.

Pressed on Johnson’s actions, she replied: “You could call it back-seat driving.” Asked if she had read the article, she took a further swipe at Johnson, replying: “Unfortunately not. I had rather a lot to do on Friday. There was a bomb that nearly went off in Parsons Green.

“Yesterday I chaired Cobra, I went to see the police. No, I didn’t have time to read the piece.”

Rudd said Scottish Tory leader Ruth Davidson “has a point” when she criticised Johnson for submitting the piece as London suffered another terror attack.

Johnson’s decision to release the article just six days before Theresa May is due to set out her plans for Brexit in a speech in Florence prompted claims in a Sunday newspaper that allies of the PM believe the move is “hostile” and “attention-seeking”.

A senior minister who backed Remain told another paper that 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, who was director of communications at Downing Street under 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”.

Liberal Democrat leader Sir Vince Cable told BBC1’s The Andrew Marr Show that May should sack the Foreign Secretary. “It’s like a school that’s completely out of control and the head teacher is sitting in her office paralysed and impotent,” he said.

“And if you’re Mr (Michel) Barnier negotiating with this government and you’ve got senior Cabinet ministers with entirely opposite views of what Britain’s negotiating position should be, what do you do?

“It is complete and absolute loss of authority and the Prime Minister on Monday morning should fire this guy, otherwise her own credibility is reduced to zero.”

But May’s de facto deputy Damian Green said Johnson would not be sacked over his intervention.

Johnson was also slapped down yesterday by the head of the UK Statistics Authority for repeating the £350 million-a-week claim.

Sir David Norgrove said he was “surprised and disappointed” by the Foreign Secretary’s decision to repeat the figure in the Daily Telegraph article. “This confuses gross and net contributions,” he wrote in a letter addressed to Johnson. “It also assumes that payments currently made to the UK by the EU, including, for example, for the support of agriculture and scientific research, will not be paid by the UK Government when we leave. It is a clear misuse of official statistics.”

Meanwhile , May flies to Canada today to seek to lay the foundations for a post-Brexit trade deal with the country. A new trade deal between the EU and Canada is due to come into effect on September 21, eliminating 98 per cent of Canadian import duties, in what Downing Street describes as a “significant boon” for UK exporters.

But when Britain leaves the EU, it will fall out of the Comprehensive Economic and Trade Agreement (Ceta), which took seven years to negotiate.

May hopes to use Ceta as a model for a new bilateral arrangement between Britain and Canada to be introduced “swiftly” after Brexit.

Under the terms of its EU membership, the UK cannot seal a free trade agreement with an outside country before its departure, though it remains unclear whether this will be possible during the “transition period” expected to last two or three years after the official date of Brexit in March 2019.

May and her Canadian counterpart Justin Trudeau are expected to agree the establishment of a new joint working group, the 13th established by the UK since last year’s referendum, to prepare the ground for a deal.