Brexit negotiations have hit a “real problem” over the issue of the Irish border, government sources have warned.
The EU is believed to be seeking further reassurances to prevent the return of a so-called hard border involving physical checks.
Hopes of a breakthrough were raised when the Brexit secretary made an unscheduled trip to Brussels on Sunday.
But talks faltered over the need for a back-up plan – known as the backstop – to avoid a hard border.
UK Prime Minister Theresa May has insisted any backstop arrangement should apply to the UK as a whole to avoid creating a new border in the Irish Sea.
But Sunday’s talks had broken down after the EU had insisted on a second backstop arrangement – just involving Northern Ireland – if the UK’s version wasn’t ready in time, Downing Street sources indicated.
The Democratic Unionist Party has vowed to oppose any new checks on goods passing between Great Britain and Northern Ireland. And the party’s Brexit spokesman has said the prospect of a no-deal Brexit is “probably inevitable”.
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Sinn Fein leader Mary Lou McDonald told BBC Radio 4’s Today programme: “It would be a chronic miscalculation and an utter disgrace if the policy of the British government was to be set by the most extreme elements of the Brexiteers and the needs and desires and the idiosyncrasies of the Democratic Unionist Party.”
This week’s summit comes as domestic political pressure on Mrs May increases amid threats of potential cabinet resignations.
Labour has called on the government to publish its plan for the backstop.
Shadow Brexit secretary Sir Keir Starmer said any proposal needed full scrutiny from MPs before an agreement could be struck with the rest of the EU at the Brussels summit.
A Number 10 source said the prime minister had made sure Parliament was regularly updated on the talks.
Former Foreign Secretary Boris Johnson said the backstop idea should be jettisoned altogether.
Writing in the Daily Telegraph, Mr Johnson said that “in presuming to change the constitutional arrangements of the United Kingdom, the EU is treating us with naked contempt”.
Meanwhile, Ireland’s ambassador to the UK, Adrian O’Neill, said Sunday’s events in Brussels were a “setback” and could increase the prospect of a no-deal Brexit.
He told BBC Radio 4’s Westminster Hour that time was “running out”, adding: “Preparations for all eventualities are ramping up quite significantly.”
Is the PM out of moves?
By BBC political editor Laura Kuenssberg
While there may have been a sense in Brussels that Mrs May was moving towards them, if anything the politics at home have become more fraught.
Thursday’s cabinet meeting ramped up concerns and gave Brexiteers another excuse to rattle their sabres.
The DUP continues its warnings that it’d sink the administration rather than see the deal it fears done. Several cabinet ministers are thinking about whether they can go on.
And, more to the point, different groups of Tory MPs with gripes about other policies are scenting opportunity as the government is so vulnerable.
Any move for the PM has become both harder, and more urgent.
Her party won’t accept a proposal to keep the UK essentially in the customs union. Parliament is likely to block no deal. The EU won’t accept her Chequers plan.
Even loyal ministers are deeply worried – “She is like a chess player who only has the king left – all she can do is move one square at a time until she is check-mated.”
The issue of the border between Northern Ireland and the Republic of Ireland, which will become the UK’s border with the EU, is one of the last remaining obstacles to achieving a divorce deal with Brussels.
In a letter to Mrs May, Scottish Secretary David Mundell and Scots Tory leader Ruth Davidson said they would not accept Northern Ireland being treated differently than the rest of the UK in any Brexit deal.
It follows reports that other top ministers have been considering their positions over the weekend ahead of a meeting of the cabinet on Tuesday at which ministers could be asked to give their consent to any agreement.
Writing in the Sunday Times, former Brexit secretary David Davis urged ministers to “exert their collective authority” and reject the plans at a cabinet meeting on Tuesday.
Brexit talks hit ‘real problem’ over Northern Ireland border}