The prime minister was accused of caving in to Spain’s demands over the future of the British overseas territory, after Madrid threatened to veto the progress of the Brexit deal due to be agreed by the EU on Sunday.
Spanish prime minister Pedro Sanchez claimed the UK and EU had conceded to its call for guarantees over Gibraltar’s status in future negotiations, so any future UK-EU trade deals would not automatically apply.
His foreign minister Josep Borrell went further, saying it was ”highly positive for Spain” and “the most important” development since Gibraltar was ceded to the UK in the 18th century.
Ms May insisted that the UK’s position on the sovereignty of Gibraltar had not changed, as she arrived for last-minute talks in Brussels on Saturday.
“The UK’s position on the sovereignty of Gibraltar has not changed and will not change,” she said.
“I am proud that Gibraltar is British and I will always stand by Gibraltar.”
Gibraltar’s chief minister Fabian Picardo also used a TV address to reject Mr Sanchez’s claims, saying: “What you have heard from the Spanish prime minister today was not a reflection of any new position, however much he tried to present it as such.”
But the row is likely to heap further pressure on the prime minister as she faces the almost impossible task of getting her deal through parliament in the face of widespread opposition.
Liberal Democrat Brexit spokesman Tom Brake was among the MPs to speak out, saying the prime minister had “caved in” and “appears to have cast the people of Gibraltar aside”.
The diplomatic spat comes after a dramatic day at home when Ms May faced renewed antipathy from her Democratic Unionist Party allies, who demanded she “bin” the deal and threatened to torpedo the confidence-and-supply agreement, which props up her government.
Potential leadership rival Boris Johnson also savaged her deal, describing it as a “historic mistake” and urging her to “junk the backstop”, a key plank of the agreement.
Tory rebels on both the Remain and Leave wings of the party are expected to join with the DUP and Labour to vote down her deal in parliament despite warnings of “potential economic chaos” from the chancellor, Philip Hammond.
Amid anger from all sides, Ms May travelled to Brussels on Saturday to meet Donald Tusk, the European Council leader, and Jean-Claude Juncker, the European Commission president.
The crunch summit was thrown into doubt by Mr Sanchez’s concerns over Gibraltar but Spain was brought back on board after an 11th-hour diplomatic push from Britain and senior EU figures.
Negotiators worked throughout the night to broker a deal to reassure Spain without reopening the withdrawal text, which both London and Brussels consider to be agreed.
The UK ambassador to the EU, Sir Tim Barrow, wrote to reassure Madrid that Gibraltar would not necessarily be covered by future trade arrangements – one of Spain’s key concerns.
Announcing the breakthrough, Mr Tusk also offered a boost to the prime minister by recommending European leaders back the Brexit deal on Sunday.
He said: “I will recommend that we approve on Sunday the outcome of the Brexit negotiations.
“No one has reasons to be happy. But at least at this critical time, the EU27 has passed the test of unity and solidarity.”
EU leaders will be asked to agree the Brexit deal and the political declaration on Britain’s future relationship with the EU on Sunday, which have been drafted after more than 18 months of wrangling.
If they give it the green light, Ms May will return to Westminster where she faces the arduous task of convincing MPs to back the plan.
DUP deputy leader Nigel Dodds delivered a brutal assessment of her plans in a speech to party faithful in Belfast, where he said the DUP would defy the prime minister if she did not change course.
It comes despite a charm offensive from Mr Hammond, who flew to Northern Ireland on Friday to woo senior party figures and business leaders over Ms May’s draft agreement.
In interviews ahead of the conference, DUP leader Arlene Foster claimed Ms May’s deal would be a worse outcome for the UK than a Jeremy Corbyn-led government – despite their longstanding differences.
She warned that her party would revisit its confidence-and-supply deal to support the Conservatives at Westminster if the Brexit agreement is voted through parliament.
Mr Johnson urged the DUP not to walk out on its confidence-and-supply agreement in a packed speech to the party’s conference in Belfast.
“Unless we junk this backstop, we will find that Brussels has got us exactly where they want us – a satellite state,” said the Tory MP.
He warned the draft Brexit deal was in danger of turning Northern Ireland into an “economic semi-colony” of the EU.
On the eve of the summit, Ms May made a direct appeal to the nation, saying her deal would deliver “for our whole country and all of our people, whether you voted ‘Leave’ or ‘Remain” and promising a “moment of reconciliation” when Britain leaves the EU.
In an open letter to the British public, Ms May said the deal will “honour the result of the referendum”, taking back control of UK borders, money and laws, and taking the country out of EU programmes “that do not work in our interest”.
She also made a plea for unity and said Brexit day next year will be “a moment of renewal and reconciliation for our whole country ... when we put aside the labels of ‘Leave’ and ‘Remain’ for good and we come together again as one people”.
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