UK government ministers will meet this afternoon to consider a draft agreement that Brexit negotiating teams have reached in Brussels and to decide on the next steps.
A spokesman for British Prime Minister Theresa May said that cabinet ministers have been invited to read documentation ahead of the meeting at 2pm.
Ministers were called into 10 Downing Street one-by-one last night to meet Mrs May.
The developments come after she told cabinet yesterday that a "small number" of issues remained to be resolved.
Her official spokesman said: "The prime minister told cabinet that since it had last met negotiations had continued in Brussels and good progress had been made.
"However, the PM said there remained a small number of outstanding issues as the UK pushes for the best text that can be negotiated."
DUP leader Arlene Foster has said the desire for a deal will not be superseded by a willingness to accept any deal, and warned Theresa May that it would oppose any Brexit deal which it believed undermined the union between Britain and Northern Ireland.
In a statement last night, she said it would be democratically unacceptable for Northern Ireland trade rules to be set by Brussels and without a clean exit clause, the UK would be handcuffed to the EU.
"I am heartened by friends of the Union on both sides of the House (of Commons) and across the United Kingdom who have pledged to stand with the DUP in opposing a deal which weakens the Union and hands control to Brussels rather than Parliament," DUP leader Arlene Foster said.
"These are momentous days and the decisions being taken will have long-lasting ramifications. The Prime Minister must win the support of the cabinet and the House of Commons. Every individual vote will count."
Earlier, the party's deputy leader Nigel Dodds said that a Brexit deal would be a very hard sell.
"The trick will be for Theresa May, can she satisfy everyone? It is going to be a very, very hard sell, I would have thought, but let's wait and see the actual detail," he said.
"The crucial issue is going to be what happens when it comes to cabinet and when it gets to parliament.
"We haven't seen any details, we'll see what happens. People know what our position is very clearly and we will judge whatever comes forward against the positions that have already been outlined."
Conservative MP Jacob Rees-Mogg has said that Mrs May's senior ministers should block her Brexit plan as it seemingly does not deliver on the vote of the British people to leave the EU.
He told the BBC: "If what we've heard is true, this fails to meet the Conservative Party’s manifesto, and it fails to meet many of the commitments that the Prime Minister makes. It would keep us in the Customs Union, and de facto in the single market.
"This is the vassal state. It is a failure of the government’s negotiating position, it is a failure to deliver on Brexit and it is potentially dividing up the United Kingdom."
Former foreign secretary Boris Johnson has said that he will vote against the deal.
He said that through the deal, the UK will stay in the Customs Union.
Mr Johnson said: "We’re going to stay in the Customs Union on this deal, we're going to stay effectively in large parts of the single market. That means it's vassal state stuff.
"It is utterly unacceptable to anyone who believes in democracy."
He added: "For the first time in a thousand years, this place, this Parliament, will not have a say over the laws that govern this country. It is a quite incredible state of affairs.
"For the first time since partition, Dublin - under these proposals - would have more say in some aspects of the government of Northern Ireland than London.
"I don't see how you can support it from a democratic point of view, I don't see how unionists can support it, and I don't see how you can support it if you believe in the economic and political freedom of this country."
MPs in the House of Commons will have access to legal analysis of any EU withdrawal agreement and the chance to question the British government's top legal advisor before being asked to vote to approve the deal, senior minister David Lidington has said.
The opposition Labour Party sought to use parliamentary procedure to force the government to publish its legal advice on leaving the EU, including on how the deal will handle the sensitive issue of the Irish border.
MPs approved the Labour motion without the need for a formal vote.
Meanwhile, London Mayor Sadiq Khan said if the deal Mrs May has "tentatively agreed with the EU27 is as we expect, it will be a bad deal for Britain which risks damaging jobs and growth for the next generation".
The London Mayor, who has been a supporter of Remain, added: "Cabinet ministers must now put aside their personal interests and ambitions and do what's in the national interest. MPs should not be supporting an agreement that damages our public services and makes it harder for our children and grandchildren.
"It's clearer than ever that the British public must now be given a say on the terms of the final deal - with staying in the European Union an option on the ballot paper.
"Nobody voted for fewer jobs and opportunities and lower economic growth - which is exactly what this deal risks delivering for London and the rest of the country."