Theresa May's Brexit plan was once again called into question after her Democratic Unionist Party (DUP) allies sent out a letter from her "Alert" warning that she could not rely on her support to push through the proposals to get the parliament.
The party accused the prime minister of breaking a promise that she would never sign a deal treating Northern Ireland differently than the rest of the UK. It was angered by a letter in which May was warned that EU negotiators continued to press for Northern Ireland to remain in the Single Market and in the Customs Union should the talks collapse.
The DUP relied on a particular paragraph – seen by the Times – in which May said it could not accept any circumstances or conditions that could put the United Kingdom customs territory into effect.
The DUP leader Arlene Foster Tweeted on Friday: "The letter from the Prime Minister is calling for alarm bells to those who value the integrity of our valuable union and those who wish a proper Brexit for the whole of the UK. Her letter indicates that the Prime Minister is in touch with the idea of a border between the Irish Sea and NI in the framework of the EU regulatory regime. "
The leak of the letter is seen by some observers as well as the DUP as part of a foundation in May for a showdown with the party over checks in British ports or factories in Northern Ireland or the UK.
According to the EU proposals, British officials would be "competent authorities" to carry out controls, but according to EU rules, the DUP will exceed its red line.
DUP MP Sammy Wilson continued to put pressure on the government and told the BBC Radio 4 program Today that the letter was sent to the party but made public by Downing Street. "I assume that it's part of the proposal to try to get public, which is finally agreed," he said.
A Downing Street spokesman said, "The Prime Minister's letter sets out her pledge that she was absolutely clear on every occasion never to accept circumstances in which the United Kingdom is divided into two customs territories. The government will not agree on anything, which will create a hard border on the Irish island. "
The EU has insisted that there is only Northern Ireland if negotiations on a broader UK approach fail. Any version of the backstop would apply unless a wider agreement between the EU and the EU on the future relationship resolved the issue of how to avoid a hard border with Ireland.
The dispute comes as it is expected that Brexit will dominate the agenda of the British Irish Council, which will be attended by Taoiseach, Leo Varadkar, David Lidington, who is actually MP of May, and Northern Irish secretary Karen Bradley. The Summit of the Isle of Man will also be attended by the first Ministers of Scotland and Wales, Nicola Sturgeon and Carwyn Jones.
Brexit is also expected to be a focal point when May meets the French President for a working lunch after visiting the ceasefire commemorations in Belgium and France.
Downing Street has rejected suggestions that a Brexit deal is imminent, after European Council President Donald Tusk had apparently indicated that a breakthrough could come within the next week.
In the meantime, Eurosceptic Conservative MPs have said they will continue to oppose the government's Brexit deal, even if May negotiates an Irish exit exit clause, former PM Steve Baker said.
The Cabinet was involved in a bitter dispute over whether and how the government could pull itself out of its backing with some concerned ministers. May's plans could put the UK in permanent suspense.