Theresa May says she “is talking to colleagues” about their concerns over the Northern Ireland “backstop” ahead of a crucial vote on her EU deal.
She suggested MPs could be “given a role” in deciding whether to activate the backstop, which is designed to stop the return of a physical border.
But she told the BBC there could be no deal with the EU without it.
No 10 has said the Commons vote will go ahead on Tuesday, despite claims it could be delayed to avoid defeat.
However, the chairman of the 1922 Committee of Conservative backbench MPs, Sir Graham Brady, told the BBC that he “would welcome the vote being deferred” until there was “clarity” on the backstop issue.
And in another development, the European Court of Justice said it would deliver a ruling on Monday on whether the UK could unilaterally cancel Brexit by reversing Article 50 – the day before the MPs’ crunch vote.
Discussions are ‘very fluid’
The government is considering an amendment to next Tuesday’s vote motion that would give Parliament more say over the backstop.
One possible option would see Parliament having a role in deciding whether to extend the transition period or enter the backstop arrangement, if no trade deal has been reached by the end of December 2020.
The transition period is due to kick-in when the UK leaves the EU on 29 March. It can only be extended once for “up to one or two years” – but if the two sides have still not agreed a deal by the end of that second period, then the backstop will apply.
This would mean Northern Ireland staying aligned to some EU rules, which many MPs say is unacceptable. The UK would also not be able to leave the backstop arrangement without EU agreement.
Another option being explored with MPs, the BBC understands, is giving Parliament an annual vote on whether to stay in the backstop, once it has been activated, or to pursue other alternatives.
The BBC’s political editor Laura Kuenssberg said discussions were “very fluid” and no decision had been reached in government about which option to choose.
Downing Street has said there is no plan to renegotiate the withdrawal agreement.
May says ‘we have a choice’
Mrs May told BBC Radio 4’s Today programme she had not given up on winning the vote on her Brexit deal – negotiated over the past 18 months or so – despite dozens of her own MPs and all opposition parties being against it.
She said she recognised concerns about the Northern Ireland border backstop keeping the UK tied to the EU indefinitely.
And she conceded the UK would have “no unilateral right” to pull out of the backstop under her EU withdrawal agreement – but she said the UK would have a choice over whether or not to enter into it.
“The backstop is something nobody wants to go into in the first place, and we will be working to make sure that we don’t go into it,” she said.
“If we get to the point where it might be needed, we have a choice as to what we do, so we don’t even have to go into the backstop at that point.”
She suggested Parliament could be “given a role” in deciding whether to enter the backstop and how the UK would get out of it.
“I recognise there are concerns from colleagues about the role of Parliament, about the sovereignty of the UK in relation to that issue, so I am talking to colleagues about how we can look at Parliament having a role in going into that and, if you like, coming out of that,” she told Today.
She again ruled out a further referendum and rejected alternative Brexit plans suggested by different factions of her party.
“None of the other arrangements that people have put forward fully deliver on the referendum. This deal delivers on the referendum,” she said.
Will May’s suggestion win over any Brexiteers?
By Laura Kuenssberg, BBC political editor
What Theresa May sketched out on Thursday was the idea of allowing MPs to choose when and if they want to go into the controversial “backstop” – the insurance policy against a hard border on the island of Ireland.
Clearly, to try to get some angry Brexiteers to change their minds, the PM is trying to give a sense that they might have more of a say.
They could, as the agreement already suggests, just extend the “transition period”, giving the two sides longer to come up with a free trade deal that would mean the dreaded backstop is never used.
It’s not surprising that MPs would have a vote on that. But Number 10 clearly hopes it will give some grumpy MPs a sense that they will have more of a say, introducing another layer of decision-making so that the backstop can be avoided.
Plan is a ‘red herring’
But reacting to the latest proposals, Brexiteer Iain Duncan Smith said that if MPs passed the EU withdrawal agreement they would not be able to change the backstop because it would be part of a “standalone international treaty”.
So MPs would be limited to saying “should we ask for an extension or should we let ourselves go in”.
Fellow Brexiteer Suella Braverman, who quit the government over Mrs May’s deal, said the PM’s proposals were a “red herring” that would be “ineffective”.
And remain supporter Phillip Lee, who also quit as a minister over the deal and now backs a further referendum, dismissed the PM’s “cosmetic concessions”.
“It’s clear that none of the big Brexit questions will be solved by this withdrawal agreement, and that the Brexit on offer is much worse than the deal we’ve already got in the EU,” he said.
The prime minister’s support has grown by one, however, after Eastbourne MP Stephen Lloyd quit the Liberal Democrat group in the Commons to vote for her deal.
Conservative Sir Nicholas Soames has also spoken up for the PM’s deal, on the the third day of debate about it in the Commons, which is focusing on the economic impact.
Ministers are arguing Mrs May’s deal creates a unique partnership with the EU, while Labour insists it will make people poorer.
The Northern Ireland’s Democratic Unionist Party, which keeps Mrs May’s government in power, has said it would support the government in a confidence motion if the deal was thrown out on Tuesday.
Sammy Wilson, the DUP’s Brexit spokesman, told Today: “Our grievance with the government has been that the government made a promise to us and to the people of Northern Ireland that Brexit would be delivered for the whole of the United Kingdom, and provided there is nothing introduced to break that promise, we have no reason to have no confidence in the government.”
But he added the DUP could still withdraw support for the government at a future date.