UK Prime Minister
Boris Johnson on Thursday suffered a blow to his hopes of getting the deal he agreed with the
European Union passed by
Britain's Parliament, when one of his party's key allies definitively said it would not vote for it.
Without the backing of
Northern Ireland's
Democratic Unionist Party (DUP), it means the pathway to a majority when Johnson takes the deal to Parliament on Saturday narrows significantly.
"We have been consistent that we will only ever consider supporting arrangements that are in Northern Ireland's long-term economic and constitutional interests and protect the integrity of the Union. These proposals are not, in our view, beneficial to the economic well-being of Northern Ireland and they undermine the integrity of the Union," Northern Ireland's DUP said in a statement.
Speaking at a joint news conference with European Commission President Jean-Claude Juncker in Brussels, Johnson told reporters that the new withdrawal agreement "represents a very good deal for both the EU and UK" and that he hoped lawmakers can "come together to get Brexit done, to get this excellent deal over the line."
It comes after the deal was announced on Twitter by Juncker, who said it "focused on the protocol on Ireland/Northern Ireland and sought to identify a mutually satisfactory solution to address the specific circumstances on the island of Ireland."
The question of the Irish border has been a major sticking point in the long negotiations and while both Johnson and the EU have agreed to the new terms, the Prime Minister's next challenge will be getting his deal approved in the UK Parliament.
Former Prime Minister Theresa May also secured a deal with the EU, but failed to pass it through the House of Commons on three occasions.
The EU's chief negotiator, Michel Barnier, said in a news conference in Brussels that the new text provides "legal certainty in every area where Brexit like any separation creates uncertainty."
He said Northern Ireland will remain aligned to a "limited" set of EU rules related to goods, that it will remain in the UK's customs territory -- but also the entry point into the EU's single market -- and the Northern Ireland assembly will be given a vote on whether to continue to apply EU rules in the region or not every four years.
Barnier added that the proposal also covers the transition period, which will run until the end of 2020 -- with the possibility to extend.
Johnson tweeted shortly after obtaining the agreement with the EU that now that Northern Ireland will remain part of the UK's customs territory, it means the "anti-democratic backstop has been abolished."
The backstop was an insurance policy designed to avoid a so-called "hard border" between Ireland and Northern Ireland if no other solution was found by the end of the transition period in 2022. It envisaged that the whole of the UK would remain tied to the EU's customs union until a trade deal was concluded between the two sides.
UK opposition parties reject Johnson's dealAfter the announcement, the UK's two main opposition parties also said they would reject the Brexit deal -- putting another spanner in the works for the Prime Minister.
Labour's Jeremy Corbyn, who leads the biggest opposition group in the House of Commons, said in a statement that Johnson's agreement was worse than what was previously agreed by May.

"This sell-out deal won't bring the country together and should be rejected," Corbyn added. "The best way to get Brexit sorted is to give the people the final say in a public vote."
The Scottish National Party and the Liberal Democrats have also opposed the deal.
The series of rejections means in order for Johnson to get the deal approved by Parliament, he'll need the support of all of his Conservative MPs, plus the 21 lawmakers he expelled after they defied him in an effort to prevent a no-deal Brexit, plus some members of the opposition.
Most estimates suggest that there are between five and 20 Labour MPs who might support a Brexit deal in defiance of their leader -- making things very tight for Johnson.
If the Prime Minister can't get parliamentary support for his plan by Saturday, he is legally obliged to write to the EU requesting a Brexit extension until January 31, 2020. He has until October 31 -- just 14 days -- until Britain is due to exit the bloc.