THERESA May does not expect Boris Johnson to resign, Downing Street has insisted, but friends of the Foreign Secretary have suggested that if the Prime Minister opts for a soft “Swiss-style Brexit,” then he will quit.

Mr Johnson, along with colleagues, will attend a special Cabinet meeting tomorrow morning to agree a collective approach before Mrs May heads to Florence to give a keynote speech on Brexit.

A No 10 source stressed that the meeting would be "a significant moment" in the process of Britain's withdrawal from the EU. He added: “We are confident the Cabinet is going in the same direction but we are not getting into conversations with Cabinet members.”

It later emerged that the Foreign Secretary is now expected to be in the audience for the PM’s speech, indicating perhaps that he is not on the brink of resigning.

His 4,000-word article at the weekend is believed to have reflected his unhappiness at early drafts of Mrs May’s speech. It was, however, condemned as “an absolute disgrace” by some senior Tories, who believe the timing of it was meant to box the PM in over what she will or will not offer Brussels in a financial settlement during the three-year transition.

Ken Clarke, the former Conservative Chancellor, said Mr Johnson should have faced the sack for his Brexit intervention.

"Sounding off personally in this way is totally unhelpful and he shouldn't exploit the fact she hasn't got a majority in Parliament, and he knows perfectly well that normally the Foreign Secretary would be sacked for doing that - and she, unfortunately, after the General Election, is not in the position easily to sack him - which he should stop exploiting," argued the veteran Europhile.

The Foreign Secretary’s article has highlighted the Cabinet split between those like Chancellor Philip Hammond, who favour an "EEA-minus" deal similar to Switzerland's involving payments for access to the single market, and those including Mr Johnson who prefer a "Ceta-plus" arrangement, involving a simple free trade deal like Canada's.

Suggestions that the Secretary of State could even resign his Cabinet post this week were dismissed as “nonsense” by his allies but they have also warned that if Mrs May offers to pay £10 billion a year into EU coffers for the privilege of gaining maximum access to the European single market during the transition, then this would be something the former London Mayor could not accept.

After suggestions that Mr Johnson was pondering resignation, he was cornered by reporters outside the lift in his New York hotel following his daily jog.

Asked if he was going to quit, he insisted: “Of course not.” Asked if there was a Cabinet split, the Foreign Secretary replied: “No, we are a government working together. We are a nest of singing birds.” He added he was confident the UK Government would "deliver a fantastic Brexit".

Mr Johnson and Mrs May were both in the United Nations building and their paths were expected to cross, albeit briefly, at a Commonwealth reception last night. Later today, the Foreign Secretary is due to be in the audience when the PM makes her speech to the General Assembly.

Asked whether she was confident that ministers at tomorrow’s Cabinet meeting would be united behind her strategy, Mrs May said: "Yes. The Cabinet is absolutely clear about the destination we are aiming for in relation to our European negotiations.

"We want to make sure we get the best possible deal for the United Kingdom as we leave the European Union.

"What we want to do is to ensure not just a good deal on trade but also on our future security and relationship on law enforcement and criminal justice."

Challenged over calls for Mr Johnson to be sacked, she said: "Boris is doing good work as Foreign Secretary. He has been doing that here at the United Nations."

The PM was careful to state that Britain would not be paying "huge sums" to the EU year after year but she also made it clear she was ready to approve continued payments for specific projects in which the UK was interested in participating in.

"What I said, if you look back at my Lancaster House speech which set out the principles of our future relationship with the European Union, is that one of the things that leaving the European Union does is it means that in the future, year on year on year, we will not be sending huge sums of money into the European Union."

Asked about the prospect of a "divorce bill" estimated to run into tens of billions of pounds, she told the BBC: "We are very clear that we are a law-abiding nation and we stand by our obligations.

"There may be projects that we want to be part of and that may involve contributing to the costs of those programmes. But these issues are part of the negotiations. Those negotiations have been very constructive," added Mrs May.

On Tuesday, she met a series of world leaders for one-on-one discussions at the UN and hosted a meeting on modern slavery attended by Donald Trump's daughter Ivanka.

Today, the PM is due to have private talks with the US President himself.