Brexit: Theresa May warned DUP of Irish sea border in case of no-deal, leaked letter suggests

Arlene Foster says PM's letter raises 'alarm bells' as Downing Street insists UK will not be 'divided into two'

Theresa May has warned her DUP allies that a customs border in the Irish sea may be written into the UK’s Brexit divorce deal, according to reports.

In a leaked letter, the prime minister tells unionist leader Arlene Foster that Brussels is pushing for the measure as a so-called “backstop to the backstop” on Northern Ireland’s customs status in case negotiations break down.

Ms May wants a deal containing a backstop measure creating a temporary “joint customs territory” with the EU for the whole of the UK.

But the bloc appears to be insisting on a fallback proposal aimed at avoiding a hard border between Ireland and the UK. This would effectively keep Northern Ireland aligned with Brussels’ customs union and single market, the letter is said to suggest.

In the letter, seen by The Times, Ms May reportedly says: “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.”

Yet the DUP has interpreted the wording to mean that the sea border clause would still be written into the divorce agreement, the paper reported.

Ms Foster said in a statement: “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.”

Ms May has been battling to agree a divorce deal with the EU that can satisfy Brussels, her own party and the DUP, whose 10 votes she will likely need to get the agreement through the House of Commons.

Asked by The Independent whether the letter explicitly said the “backstop to the backstop” would be included in any Brexit agreement, a Downing Street spokesperson declined to comment.

Number 10 said in a statement: “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.”

The Irish backstop, a plan to keep the UK in regulatory alignment with the EU, was devised as a method to maintain the soft border if Britain leaves the bloc without a wider deal.

However, the “backstop to the backstop” has been proposed as something of an insurance policy for Brussels, creating a customs border in the Irish Sea and maintaining regulatory alignment between Northern Ireland and the EU if the rest of the UK leaves the single market.

Sam Lowe, from think tank the Centre for European Reform, said supporters of a “hard” Brexit may find some form of regulatory barrier between Northern Ireland and the British mainland an acceptable trade-off.

“My feeling is that, at some point, the hard Brexiters (who we already know prioritise Brexit over NI, because they voted for Brexit), will decide that NI having a distinct relationship with the EU is a price worth paying,” he tweeted.

Taoiseach Leo Varadkar, Mrs May’s effective deputy prime minister David Lidington and Northern Ireland secretary Karen Bradley will attend a summit on the Isle of Man on Friday.

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.

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 UK government source said that reports in the European media that a deal could come in the next few days should be taken “with a very large pinch of salt”.

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 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 access to UK waters for its trawlers, the newspaper said.

Additional reporting by PA