A BITTER row with the DUP left Theresa May unable to deliver any progress to EU leaders on Brexit talks – prompting them to reject her Chequers plan.

Ministers are in secret negotiations with the Ulster unionist party over a new bid by the PM to break the negotiations deadlock, The Sun has learned.

6 The PM has been left unable to deliver any progress to EU leaders - prompting their rejection of Chequers Credit: Paul Grover

Furious Prime Minister Theresa May slams EU over lack of respect and issues warning in barnstorming address after Salzburg Brexit summit

Mrs May wants to establish a different system of rules for goods in Northern Ireland than Great Britain as the missing part of a backstop plan to ensure the Irish border remains open.

But DUP leaders are refusing to agree the move, which they argue would split up the United Kingdom.

And any extra regulatory barriers without the Northern Irish people’s express consent would be a serious breach of the Good Friday peace agreement, they insist.

A senior DUP source told The Sun: “We have told Theresa that we will never allow her to divide up the UK’s single market, and we will never budge on that”.

6 Nigel Dodds said the DUP are 'engaging with the Government regularly and intensely' Credit: Getty Images - Getty

No10 must get the full backing of the unionist party’s 10 MPs or Mrs May’s wafer thin Commons majority will disappear.

The PM’s failure to deliver the final part of the Northern Ireland backstop to EU leaders at a summit in Salzburg lead them to lash out at her and kill her Chequers plan, Brussels sources have claimed.

Irish Taoiseach Leo Varadkar was alleged to have begged her to produce a finished plan to take pressure off him from opponents in Dublin.

Instead, Mrs May promised to bring forward the proposals “soon”.

The DUP’s Westminster leader Nigel Dodds said: “The DUP continues to engage with the Government regularly and intensely at all levels to hold the Government to its commitments”.

6 The PM's Chequers or nothing approach has angered EU leaders Credit: Getty Images - Getty

Prime Minister Theresa May talks Chequers Deal and Northern Ireland border issue ahead of Salzburg talks

Mrs May’s pitch to EU leaders to win them round to her Chequers deal at a dinner on Wednesday night was also claimed to have been disastrous.

One EU diplomatic described it as “bizarre”, and accused her of just reading out an article to them that she had penned in German newspaper Die Welt earlier in the week.

No10 aides insisted the claim was false, but conceded the PM had used speaking notes to address the 27.

Mrs May’s “Chequers or nothing” ultimatum to the leaders – delivered in an interview with BBC Panorama on Monday – also angered them.

6 Michel Barnier gave a detailed criticism of the economic section in the Chequers plan Credit: EPA

And the final nail in the coffin was a detailed annihilation of the economic part of the Chequers proposal from EU chief negotiator Michel Barnier over a lunch meeting of the 27 leaders without Mrs May on Thursday.

The Frenchman gave specific examples of how Britain’s plan would decimate the EU’s steel and chemical industries, according to sources.

He also explained how the Commission was compromising on the EU version of the backstop, hours after Mrs May had curtly rejected it outright.

A senior diplomatic source told The Sun the “stark contrast” between the performances of the PM and Mr Barnier had persuaded leaders to act.

6 The pitch to EU leaders to win them round to her Chequers plans was said to be disastrous for the Prime Minister Credit: Getty Images - Getty

They said: “He managed to convince them Chequers can’t work like it’s written. They all believed him, that he really was genuinely trying to find solutions.

“It was triggered during the debate that people thought no, we have to move on now.

“Because if we don’t move on in October we’ll arrive in November with zero progress. Then we’re just organising a failure for November.”

On Mrs May’s humiliating day, they added: “There was no ambush. There was a mismanagement of expectations on the UK side about what would happen.”

6 The DUP are refusing to accept the PM's idea of keeping the Irish boarder open Credit: PA:Press Association

Recent briefings by Number 10 about splits in the EU, plus warm overtones towards the UK from Poland and Hungary, hardened leaders’ resolve.

The 27 leaders had arrived in Salzburg originally wanting to help Mrs May by choreographing a soft landing for a Brexit deal.

An EU official added: “It’s true there was an expectation of de-dramatisation going into this summit and we saw that with Barnier offering a new version of a backstop beforehand.

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“That got offered to de-dramatise but that was undermined by the op-ed Theresa May published, and to an EU audience as well, where she completely dismissed the proposed Irish backstop and put things back into the sovereignty narrative.

“We are concerned a little bit that the British game plan here is to push the backstop to the very end.”