Boris Johnson will not be sacked over his extraordinary 4,000-word intervention into the Government’s approach to Brexit, according to Theresa May’s closest ally in Government, Damian Green.

Mr Green, the First Secretary of State and de facto deputy Prime Minister, also attempted to play down splits in the Cabinet and urged people to “calm down” over Mr Johnson's Daily Telegraph article, which was interpreted as leadership bid or a prelude to a resignation.

When asked on Sky News’s Sunday with Paterson whether Mr Johnson would be sacked over the unprecedented intervention – just six days before Ms May’s major Brexit speech in Florence on Friday – Mr Green replied: “No he isn’t.

“And the reason is he, like the rest of the Cabinet, like the Prime Minister, is all about wanting to get the best deal for the British people.”

“I’ve read Boris’s article and I can’t say there was anything surprising in it. Boris is an optimist – he argued his case eloquently during the referendum campaign that he thought Brexit was a great opportunity for this country and that is what is in that article.”

While many of the Foreign Secretary’s colleagues believed the article to be an attempt to undermine the Prime Minister’s authority and destabilise the Government, Mr Green urged “everyone to calm down”.

“I do think we’re having a weekend of excitement over the timing of it – just before the Prime Minister’s speech. I read the article and there’s nothing in it that contradicts the Lancaster House speech.”

But speaking shortly before Mr Green, the Home Secretary Amber Rudd accused the Foreign Secretary of “backseat driving” the Brexit process and criticised him for publishing the article on the same day of a suspected terrorist incident in London.

Also appearing on the BBC’s Andrew Marr Show, the Liberal Democrat leader Sir Vince Cable said the Foreign Secretary’s comments placed the Prime Minister in “an impossible position”.

Brexit: the deciders Show all 8 1 /8 Brexit: the deciders Brexit: the deciders European Union's chief Brexit negotiator, Michel Barnier Getty Brexit: the deciders French President Emmanuel Macron Getty Brexit: the deciders German Chancellor Angela Merkel Reuters Brexit: the deciders Commission President Jean-Claude Juncker EPA Brexit: the deciders The European Parliament's chief Brexit negotiator Guy Verhofstadt Getty Brexit: the deciders Britain's Prime Minister Theresa May Getty Images Brexit: the deciders Britain's Chancellor of the Exchequer, Philip Hammond PA Brexit: the deciders After the first and second appointed Brexit secretaries resigned (David Davis and Dominic Raab respectively), Stephen Barclay is currently heading up the position PA

“I just don’t understand why she hasn’t fired him,” Sir Vince added. “It’s like a school that’s completely out of control and the headteacher is sitting in her office paralysed and impotent.

“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?