Theresa May faces a "challenging vote" when her Brexit deal is put before MPs, the new Brexit secretary has admitted, as the EU's top official warned that the only alternative was leaving without one at all.
But Stephen Barclay said the Prime Minister has managed to get the best agreement possible for the United Kingdom after her two-year-long negotiation with Brussels.
Mrs May will face the Commons after EU leaders endorsed the deal at a summit on Sunday, and made it clear it was not up for renegotiation.
She will tell MPs "with absolute certainty" that "there is not a better deal available", and challenge them to back her plan or risk crashing out without an agreement.
The PM will warn her Cabinet at a meeting on Monday morning that rejecting her deal will "open the door to more division and uncertainty, with all the risks that will entail".
'The national interest'
But after scores of MPs have declared their intention to vote it down, her Brexit Secretary was asked on BBC Radio 4's Today programme how the Government will get it through Parliament.
Mr Barclay, who only took over the role from Dominic Raab earlier this month, said: "Well, it's going to be a challenging vote.
But it's now the job of all of us in Cabinet to make the case to our colleagues, make the case to the country.
"The Prime Minister, after two years working day and night in the national interest, has secured a deal that respects the referendum result, and does so in a way that also protects jobs, that also gives security to EU citizens."
He said people needed to know what the choice now facing Britain was, adding: "The choice is between a deal, or the uncertainty that would flow from what the Chancellor said last week; the choppy waters that we will move in to if this deal does not go through."
Speaking on the same programme, European Commission president Jean-Claude Juncker said there will be no more negotiation on the Brexit agreement, insisting: "This is the best deal for Britain."
He reiterated his comments from the weekend, saying: "And this is the only deal possible, so if the House (of Commons) says no, we would have no deal."
He added: "It's not the intention of the Prime Minister, the Cabinet, nor of the Parliament to go for a second referendum. This is the deal."