Britain is to have talks with the EU over the coming days about how to obtain "further assurances" which might persuade MPs to back the Brexit Withdrawal Agreement, Theresa May has said.
In a press conference at the end of a European Council summit in Brussels, the Prime Minister acknowledged that it would not be possible to reopen the agreement to alter the backstop provisions which have sparked mass rebellion among Tory MPs.
She confirmed she had a "robust" discussion with European Commission president Jean-Claude Juncker and insisted she had been "crystal clear" about the UK's need for firmer assurances that the backstop cannot become permanent.
Video footage of the conversation showed a clearly angry PM apparently berating Mr Juncker for saying that her address to leaders of the 27 remaining states on Thursday evening had been "nebulous".
She told the press conference: "I had a robust discussion with Jean-Claude Juncker - I think that's the sort of discussion you're able to have when you have developed a working relationship and you work well together.
"And what came out of that was his clarity that actually he'd been talking - when he used that particular phrase - he'd been talking about a general level of debate."
Mrs May welcomed the official conclusions issued by the EU27 which committed the EU to trying to get a post-Brexit trade deal agreed quickly enough to avoid the need for a backstop to keep the Irish border open.
"As formal conclusions, these commitments have legal status and therefore should be welcomed," she said.
But she added: "The EU is clear, as I am, that if we are going to leave with a deal, this is it.
"But my discussions with colleagues today have shown that further clarification and discussion following the council's conclusions is in fact possible.
"There is work still to do and we will be holding talks in coming days about how to obtain the further assurances that the UK Parliament needs in order to be able to approve the deal."
Juncker: 'I would like clarifications'
Mrs May's hopes of a legally binding commitment on the backstop from the EU27 were dashed on Thursday, when Mr Juncker said there could be "no real changes" to the Withdrawal Agreement negotiated over 18 months.
Council president Donald Tusk said the leaders had expressed a "firm determination" to work "speedily" to ensure there is an agreement on the future relationship in place by the time the transition period ends in December 2020, so the backstop is not needed.
But Mr Juncker criticised Mrs May's lack of clarity over what she was seeking from the future relationship.
"Our UK friends need to say what they want, instead of asking us to say what we want," he said.
"So we would like, within a few weeks, our UK friends to set out their expectations for us because this debate is sometimes nebulous and imprecise and I would like clarifications."
He added: "We don't want the UK to think there can be any form of renegotiation, that is crystal clear. We can add clarifications but no real changes.
"There will be no legally binding obligations imposed on the withdrawal treaty."