BRUSSELS (Reuters) – The European Union is ready to give Britain the unilateral right to leave the bloc’s customs union, chief negotiator Michel Barnier said on Friday, in a bid to make the Brexit deal acceptable to the UK parliament.

He stressed, however, that Britain would still need to honour its commitment to preserve a border free of controls between EU member Ireland and the British province of Northern Ireland – something that in previous negotiations led to proposals to place a customs border “in the Irish Sea”, between the island of Britain and its province.

Just three weeks before Britain is due to leave the EU on March 29, the divided UK parliament has yet to approve the EU-UK Brexit deal. British Prime Minister Theresa May called on the bloc on Friday to make “one last push” to break the deadlock. [nL5N20V2XP]

At the heart of the House of Commons’ opposition to the already-negotiated divorce deal is the so-called “backstop”, a provision to keep the sensitive Irish border open after Brexit, which the eurosceptic wing of May’s Conservative party fears could trap the UK in the EU’s trading rules forever.

“EU commits to give UK the option to exit the Single Customs Territory unilaterally, while the other elements of the backstop must be maintained to avoid a hard border,” Barnier tweeted after briefing ambassadors of the 27 EU states that are staying on together after Brexit.

“UK will not be forced into customs union against its will,” he added.

As Brexit goes down to the wire, fears on both sides of the Channel are growing about the economic damage in the event that Britain leaves the EU abruptly without any transition agreement to soften the resulting disruption to trade.

While Barnier’s latest proposal would make legally binding commitments of the assurances the EU offered to London in January, it is unlikely to be seen as enough by many of the harder eurosceptics in May’s Conservative party, which has no majority in parliament.

“The EU will continue working intensively over the coming days to ensure that the UK leaves the EU with an agreement,” Barnier said, as British and EU negotiators held more talks on Friday.

They were due to continue through the weekend.

Barnier said the bloc was ready to legally commit to using its “best endeavours” in trade negotiations with Britain after Brexit to find a solution that made sure the Irish border remained open, and the contentious backstop was never applied.