Boris Johnson has opened up an astonishing new Government split with a crude outburst against Theresa May’s new Brexit policy.

The Foreign Secretary stunned fellow Ministers with his four-letter dismissal of the Prime Minister’s plan at Friday’s special Chequers summit designed to unite the Cabinet. His comment risks making him the first victim of Mrs May’s fresh crackdown on dissent.

Mr Johnson – who has been accused of betrayal by Tory Brexiteers for not blocking Mrs May’s ‘soft Brexit’ proposals – spoke out against the plan for the UK to remain in line with Brussels rules in a new free trade zone with the EU.

Boris Johnson, pictured left, stunned fellow ministers with a four-letter dismissal of Theresa May's Brexit plan during Friday's Chequers meeting after Mrs May, right, called for loyalty

According to a reliable source, he complained that anyone obliged to defend the proposals would be ‘polishing a turd’.

He added sarcastically: ‘Luckily we have some expert turd polishers’ – shooting a glance at one of Mrs May’s spin doctors.

Challenging the Prime Minister’s new policy to her face, he said that her decision to try to ‘align’ UK trading rules with the EU would reduce Britain to the humiliating status of a ‘vassal state’.

He also took issue with her cher-ished new customs plan, the Facilitated Customs Arrangement (FCA), claiming it would be a ‘serious inhibitor’ to striking new trade deals with non-EU countries.

His outburst was revealed just hours after Mrs May tried to draw a red line under weeks of open dissent from her Ministers, vowing that from now on she will enforce collective Cabinet responsibility and sack any Ministers who defy her. Some senior Tories believe she may be forced to fire Mr Johnson.

The outburst was revealed hours after Mrs May threatened to sack disloyal ministers

A Mail on Sunday poll today endorses her handling of the Cabinet showdown, with 33 per cent of voters supporting her Brexit plan and 23 per cent opposing it. The Survation poll, the first survey since the Chequers summit, suggests Mrs May has twice the support of Mr Johnson – although voters do not believe her plan is ‘faithful’ to the EU referendum result.

Last night, Eurosceptic Tories said there was so much anger at the PM’s ‘sell-out’ that some MPs would submit no-confidence letters to force a challenge to her leadership.

And Jacob Rees-Mogg’s pro-Brexit European Research Group said experts believe the Chequers deal left the UK ‘on course for a “black hole” Brexit’ – meaning we would be sucked into the orbit of EU rules with no hope of escape.

Boris Johnson has launched an extraordinary four-letter attack on PM Theresa May over her Brexit plans

Mr Johnson made clear in the run-up to Friday’s session that he was vehemently against any scheme which left us shackled to EU rules, leading to fears in Downing Street that he and other pro-Brexit Ministers could resign.

But Mrs May launched her own plan to kill off his revolt: signalling in advance she had already lined up ‘talented’ junior Ministers to replace any Cabinet quitters; forcing all those at the summit to hand over their phones to stop them briefing against her under the table; and issuing an official No 10 communique declaring victory while her critics were still stuck inside arguing.

Last week, Boris attacked businesses for undermining Brexit

This newspaper understands that seven out of the 30 Ministers at the summit spoke out against the plan. Mr Johnson left Chequers after dinner late on Friday evening in the back of a Government car, having chosen not to resign. But his position prompted hardline Brexiteer Andrew Bridgen to liken Mr Johnson’s approach to Neville Chamberlain’s appeasement of Hitler.

Writing in today’s Mail on Sunday, the outspoken Conservative MP says: ‘We needed Boris to emulate his hero Churchill. Instead, he gave us a modern-day version of Neville Chamberlain.’

But an ally of Mr Johnson hit back: ‘Boris has acted with total propriety. He told the Prime Minister his views openly. There is nothing new in him expressing himself in robust and colourful language. There is no offence in that.’

When asked why Mr Johnson had not resigned, a supporter of the Foreign Secretary said: ‘Boris is of more use to the country inside the Cabinet because it will enable him to stop a soft Brexit getting any softer. The only person who would benefit from him leaving Cabinet would be Michel Barnier [the EU’s chief Brexit negotiator].

‘By staying, Boris can carry on making the argument for the Brexiteers. But he supports collective Cabinet responsibility and will abide by it. He will not be speaking out publicly against the proposals.’

A supporter of the Foreign Secretary, when asked why he hadn't resigned, claimed 'Boris is of more use to the country inside the Cabinet because it will enable him to stop a soft Brexit getting any softer'

No 10 sources claim that Mr Johnson was ‘engaged’ and ‘constructive’ throughout the day. They claimed his comment about ‘polishing a turd’ was light-hearted and denied he said Mrs May risked making the UK a ‘vassal state’ of the EU.

Drilling down into deal's specifics What would Theresa May’s plan mean for post-Brexit trade? Under a new UK-EU free trade deal, the UK would abide by EU regulations for industrial, agricultural and food goods. The UK’s services sector would lose its current levels of access to EU markets. How would the Facilitated Customs Arrangement (FCA) work? All imported goods would be charged the UK tariff at the border, rather than the EU rate. Goods would then be tracked – and if they were sent on to the Continent, then the EU tariff would be charged and the money passed on to Brussels. No10 says the plan allows the UK to sign trade deals with other countries. What would be the impact on UK sovereignty? Parliament would have the final say over how EU rules were incorporated into UK law, but would have to pay ‘due regard’ to European Court of Justice rulings relating to the trade in EU goods Will the deal lead to a drop in immigration? Freedom of movement as it stands will come to an end, but an as yet undefined ‘mobility framework’ will ensure that UK and EU citizens can continue to travel to each other’s territories to apply for study or work. Advertisement

But he is not alone in his denunciation of Mrs May’s FCA plan. One of Brexit Secretary David Davis’s aides said: ‘It is called the FCA because it is a “f*** up”.’

The drama could revive the tension between Mr Johnson and fellow Brexit campaigner Michael Gove, who infamously betrayed Mr Johnson in the 2016 Tory leadership contest. In contrast with Mr Johnson, the Environment Secretary helped swing the Cabinet behind Mrs May’s plan, leaving Boris outgunned. A source close to Mr Gove described his interventions on Friday as ‘pragmatic’, saying: ‘It’s going too far to say Michael was cheerleading for May’s plan.

‘His view was that given that the party does not have a Commons majority, and that the EU is playing hardball, her proposal is probably the best on offer.’

After dinner on Friday, the Prime Minister gave a short speech in which she hailed a ‘historic day’ and paid a warm tribute to Mr Davis for leading the negotiations.

Mr Davis briefed Mr Barnier on the Chequers proposal yesterday.

Although Mr Barnier has cautiously welcomed the proposals in public, senior EU figures have privately repeated warnings that the UK cannot ‘cherry pick’ and stay in the single market for goods without allowing sweeping freedoms for EU citizens to enter the UK.

Last night, Mrs May said that her plan was ‘a good deal for Britain and a good deal for our future’.

She added that her plan would spell an end to free movement of people; the jurisdiction of the European Court of Justice in the UK; and ‘vast sums’ of money going to Brussels – and Britain taking ‘control of our money, laws and our borders’.

Labour leader Jeremy Corbyn challenged her to hold a General Election if she failed to get agreement on the new Brexit plan and said the Chequers agreement ‘might unravel in a few days’.

Politician with a penchant for fruity language Theresa May is just the latest person to have felt the full force of Classics scholar Boris’s ripe rhetoric – often laced with four-letter words. Two weeks ago it emerged he dismissed business fears about Brexit saying ‘f*** business.’

At the same time he said the UK was heading for a ‘bog roll Brexit.’

In February he was seen muttering ‘b******s’ at Jeremy Corbyn in the Commons.

In 2017 he lashed out at ‘Leftie tossers’ on a visit to Bristol

In 2016 he caused outrage in Turkey by penning a limerick with the rhyme ‘Ankara’ and ‘w***erer.’

In 2015 he told a taxi driver to ‘f*** off and die.’ Advertisement

Boris Johnson thinks he's Churchill - but this so-called Brexit deal proves he's really Chamberlain, writes ANDREW BRIDGEN

Tory MP Andrew Bridgen has accused Boris Johnson of raising the white flag over Brexit

This so-called Brexit deal is nothing short of a betrayal of the 17.4 million people who voted to leave the EU. What on earth were the staunch Leavers in the Cabinet doing?

Where was Boris Johnson? At Chequers on Friday, we needed him to emulate his hero, Winston Churchill. Instead, he gave us a modern-day version of Neville Chamberlain.

Sadly, the Foreign Secretary was not alone in apparently waving the white flag of appeasement in the direction of Brussels. Other Brexiteer buccaneers and recent Brexit converts also jumped ship.

The door to Mrs May’s country residence was open but they chose not to walk out of it. Perhaps the threat of the withdrawal of the Government limo was just too great.

This is a huge mistake on two grounds. Firstly, all those harbouring leadership hopes have done their ambitions fatal harm. Grassroots party members will have no truck with their perceived treachery. Some will try to keep their leadership hopes alive by claiming it was not the time to quit and they had a duty to stay on to ensure Brexit is not further watered down. But it leaves only one credible contender with the integrity and backbone to follow Mrs May: Jacob Rees-Mogg.

Secondly, Brexiteer Cabinet Ministers are losing their nerve at the wrong time. This is not the end of the battle – it is the start of the real fight for a true Brexit. What Theresa May unveiled last week appears little short of a punishment Brexit, designed by the EU to dissuade any other country from leaving the bloc.

With no incentive to offer non-EU countries free trade deals when we leave, through mutual recognition of standards, the UK will forever remain a captive market for overpriced EU goods. It means going through the pretence of leaving but becoming a non-voting associate member, a vassal state.

We would still be locked into the EU’s suffocating embrace via this ‘common rule book’ while the dead hand of the European Court of Justice will be lurking in the background.

In contrast, we should call Brussels’ bluff and, if necessary, leave without a formal deal. A so-called ‘no deal’ scenario may sound scary but ‘no deal’ does not actually mean no deal. It simply means the UK would trade on WTO terms which we use already to trade with most of the world.

The fight to deliver a proper Brexit starts here and now.