The Democratic Unionist Party said it appeared the Prime Minister was prepared to break her promise never to agree a deal which could separate Ireland from the UK.
The European plan would leave Northern Ireland tied to the single market and customs union if Brexit talks collapse. Mrs May has previously insisted no UK prime minister could ever agree to such proposals.
However, Brussels has demanded an insurance policy to avoid a hard border in Ireland.
Mrs May has previously insisted no UK prime minister could ever agree to such proposals
The PM’s five-page letter, leaked to The Times, was sent on Tuesday to Arlene Foster, the DUP leader, and Nigel Dodds, her deputy.
Mrs May says in the letter that the EU is still pushing for a ‘backstop to the backstop’. But she stresses that she would never allow a divide between Northern Ireland and Britain to ‘come into force’.
This wording has been interpreted by the DUP to mean the clause will nevertheless be inserted into the legally-binding agreement, the paper reported.
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.’
Mrs Foster said: ‘The Prime Minister’s letter raises alarm bells for those who value the integrity of our precious Union’
Mrs May needs the ten DUP votes to help get her Brexit plan through the Commons. Last night a Downing Street spokesman said: ‘The Prime Minister’s letter sets out her commitment…to never accepting any circumstances in which the UK is divided into two customs territories.’
Jacob Rees-Mogg told The Times: ‘None of this works at all. To say, “because I’ve been incompetent in the negotiation so far I’m going to have to agree to a final backstop that could undermine the integrity of the UK, but go on to say, trust me because I’ll be more competent in my future negotiation than I have in the ones to date”, is a line that lacks credibility.’
Sam Lowe, from the Centre for European Reform, said the acceptance of a backstop is good news for withdrawal negotiations but agreed it will cause tensions between the prime minister and the DUP.
It came as Mrs May embarked on a diplomatic tour of Europe as she raced to get a Brexit deal ready to present to her Cabinet as soon as Monday. She will hold meetings today with French president Emmanuel Macron and Belgian prime minister Charles Michel.
EU chiefs yesterday suggested a Brexit deal could be finalised by the start of next week – paving the way for it to be rubber-stamped by leaders at a special summit on Sunday, November 25.
A Downing Street spokesman told The Time last night: ‘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.’
In February, Mrs May told the Commons that a draft deal by the EU “would, if implemented, undermine the UK common market and threaten the constitutional integrity of the UK by creating a customs and regulatory border down the Irish Sea, and no UK prime minister could ever agree to it”.