British Prime Minister Theresa May was in Brussels on Saturday for last-minute talks with European Commission President Jean-Claude Juncker and European Council President Donald Tusk on the eve of an EU summit threatened by Spanish objections to her deal on Britain's withdrawal from the bloc.

Spain had threatened to veto the deal unless the wording was changed to give Madrid guarantees that it alone can decide on the future of the disputed territory of Gibraltar in direct talks with London.

However, an agreement reached on Saturday between Spain, the EU and Britain removed obstacles to the summit, both sides said.

"We have reached an agreement on Gibraltar," said Spanish Prime Minister Pedro Sanchez in a statement. Any future decisions about Gibraltar would be taken only with Spain's consent, he said.

EC spokesman Margaritis Schinas confirmed that after a constructive meeting between Juncker and May, EU leaders were "on track for tomorrow" and the key summit.

President @JunckerEU and Prime Minister @theresa_may conclude a constructive meeting. We are on track for tomorrow. #Article50 #Brexit

— Margaritis Schinas (@MargSchinas) November 24, 2018

Deal in 'our national interest'

May hopes to leave Brussels on Sunday with the terms of the British withdrawal on March 29 and a comprehensive concept for future Britain-EU relations settled with the bloc.

In an open letter to the UK people, she said she would campaign vigorously for British lawmakers to vote in favor of the main withdrawal agreement when it comes before Parliament.

"It will be a deal that is in our national interest — one that works for our whole country and all of our people, whether you voted 'Leave' or "Remain,'" she said late Saturday.

Northern Irish opposition

The British premier, however, is still facing significant opposition to the deal. The Democratic Union Party (DUP) of Northern Ireland, whose support is vital to her government, has said the deal would leave Britain in a "pitiful and pathetic place."

The right-wing, "Christian fundamentalist" DUP, which is in favor of British rule in Northern Ireland, believes the deal's backstop provision to ensure an open border on the island of Ireland will give the province a different economic status compared with the mainland.

DUP leader Arlene Foster told delegates at a party conference on Saturday that the backstop must be removed, otherwise the party will vote against the withdrawal agreement if it is brought before Parliament.

The DUP fears the measure could increase the chances of Irish unification, which it vigorously rejects.

Getting the DUP on board will be highly important to May if the deal is to be passed by Parliament, where May's Conservative Party only has a minority. The Conservatives have a "confidence-and-supply" arrangement with the DUP's 10 members of Parliament, allowing them an effective majority.

Britain's finance minister, Philip Hammond, reiterated his support for May's draft deal on Saturday, telling broadcaster BBC that it was "a way of Britain leaving the European Union ... with minimum negative impact on our economy."

At the same time, he warned that no deal would mean "very serious" consequences in the future for the economy, jobs and prosperity.