By David Hughes, Press Association Chief Political Correspondent
Theresa May’s Brexit plans have been dealt a blow as her Democratic Unionist Party allies hit out at fears that a deal could impose barriers between Northern Ireland and Great Britain.
DUP leader Arlene Foster said the Prime Minister appeared “wedded to the idea of a border down the Irish Sea” despite Downing Street’s repeated assurances to the contrary.
The response of the DUP has caused frustration in Downing Street, with sources insisting that Mrs May was not hiding behind “weasel words” and had stressed that she would not accept a deal which saw Northern Ireland hived off.
The European Union’s fallback proposal aimed at avoiding a hard border between Ireland and the UK would effectively keep Northern Ireland aligned with Brussels’ customs union and single market.
A leaked letter from the Prime Minister in reply to an earlier message from Mrs Foster and her deputy, Nigel Dodds, set out Mrs May’s approach.
She wants a “backstop” measure which would create a temporary “joint customs territory” with the EU for the whole of the UK.
But Brussels appears set to insist on a Northern Ireland-only “backstop to the backstop” in case negotiations on a wider UK approach break down or any time limit on it expires.
In the letter, obtained by the Times, Mrs May said: “I am clear that I could not accept there being any circumstances or conditions in which that ‘backstop to the backstop’, which would break up the UK customs territory, could come in to force.”
But she acknowledged that the “unique circumstances” of Northern Ireland “could require specific alignment solutions in some scenarios” on regulations.
The scope of any alignment with Brussels’ rules would be limited to what is “strictly necessary” to avoid a hard border.
The DUP has interpreted the wording of her letter to mean that Northern Ireland-only measures will be contained in the Brexit divorce deal despite Mrs May’s insistence it will never come into effect.
Mrs Foster said: “The Prime Minister’s letter raises alarm bells for those who value the integrity of our precious union and for those who want a proper Brexit for the whole of the UK.
“It appears the Prime Minister is wedded to the idea of a border down the Irish Sea with Northern Ireland in the EU single market regulatory regime.”
DUP Brexit spokesman Sammy Wilson said “we want to trust the Prime Minister” but “you have to judge any promise by what is actually delivered in an agreement”.
He told BBC Radio 4’s Today programme that the letter “makes it quite clear the Government has accepted there will be a Northern Ireland-only backstop, that that backstop will require specific alignment for regulations” without Northern Ireland being given a say.
“That, to us, is a breach of the promise which has been made that we would not be cut off from the rest of the United Kingdom,” he said.
The Prime Minister relies on the support of the DUP’s 10 MPs for her Commons majority, votes which may become crucial as she attempts to get a deal through Parliament.
A Downing Street spokesman said: “The Prime Minister’s letter sets out her commitment, which she has been absolutely clear about on any number of occasions, to never accepting any circumstances in which the UK is divided into two customs territories.
“The Government will not agree anything that brings about a hard border on the island of Ireland.”
Any version of the backstop would apply unless and until a wider UK-EU deal on the future relationship solved the issue of how to avoid a hard border with Ireland.
Downing Street has played down suggestions that a Brexit deal is imminent, after European Council president Donald Tusk appeared to indicate a breakthrough could come within the next week.
A senior source said: “It does not feel to me like things are going to move today.”
Cabinet ministers have been on stand-by for an emergency session to review any potential deal, but the source said that “nothing is going to happen” in terms of a meeting over the weekend.
A potential sticking point could be demands for EU fishing fleets to be given continued access to British coastal waters as the price for agreeing to Mrs May’s UK-wide backstop, the Daily Telegraph reported.
A UK-wide customs deal would maintain quota-free and tariff-free access to European markets for the British fishing industry and in return the EU wants to keep continued access to UK waters for its trawlers, the newspaper said.
Ireland’s Taoiseach Leo Varadkar, Mrs May’s effective deputy prime minister David Lidington, and Northern Ireland Secretary Karen Bradley were attending a summit in the Isle of Man.
Brexit is expected to dominate the agenda of the British Irish Council, which also involves the first ministers of Scotland and Wales, Nicola Sturgeon and Carwyn Jones.