British Prime Minister Theresa May is to go back to the EU to try to renegotiate her Brexit deal after MPs gave their backing to proposals to replace the backstop.
However, she earned an immediate rebuff from Brussels, where European Council president Donald Tusk insisted that the Withdrawal Agreement struck last November was not open for renegotiation.
The Irish Government has also reiterated that the EU position on the Withdrawal Agreement has not changed.
Meanwhile, one of Mrs May's strongest negotiating weapons was ripped from her hands by MPs who voted to block a no-deal Brexit.
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In a night of high drama at Westminster, the Commons voted by 317 to 301 in favour of a proposal backed by Mrs May to reopen the Withdrawal Agreement and replace the backstop with "alternative arrangements" to avoid a hard border in Ireland.
Mrs May said that the result showed there was a means of securing a "substantial and sustainable majority in this House for leaving the EU with a deal" and vowed to seek a new agreement with Brussels.
But in a statement, Mr Tusk's spokesman said: "The Withdrawal Agreement is and remains the best and only way to ensure an orderly withdrawal of the UK from the European Union. The backstop is part of the Withdrawal Agreement, and the Withdrawal Agreement is not open for re-negotiation."
And French President Emmanuel Macron also said the agreement was "not renegotiable", in comments just moments before MPs voted.
Theresa May says the UK will seek 'legally binding changes to the Withdrawal Agreement that deal with concerns on the backstop' pic.twitter.com/fF0sPgDPIO— RTÉ News (@rtenews) January 29, 2019
The Commons approved a cross-party amendment, tabled by Midlands MPs Caroline Spelman and Jack Dromey, rejecting a no-deal Brexit by 318 to 310.
The vote is not legally binding on the Government but will impose massive political pressure on the Prime Minister to delay Brexit from its scheduled date of 29 March if she cannot secure a new deal from Brussels.
She told MPs: "I agree that we should not leave without a deal. However, simply opposing no-deal is not enough to stop it.
"The Government will now redouble its efforts to get a deal that this House can support."
There was uproar in the chamber as she said: "There is limited appetite for such a change in the EU and negotiating it will not be easy. But in contrast to a fortnight ago, this House has made it clear what it needs to approve a withdrawal agreement."
Mrs May said she would seek "legally binding changes to the Withdrawal Agreement that deal with concerns on the backstop while guaranteeing no return to a hard border".
And she told MPs: "If this House can come together, we can deliver the decision the British people took in June 2016, restore faith in our democracy and get on with building a country that works for everyone.
"As Prime Minister I will work with members across the House to do just that."