The European Council president has said that if Theresa May's Brexit deal is rejected by MPs the UK will face a no-deal Brexit, or no Brexit at all.
Donald Tusk made the announcement at the G20 summit in Argentina, suggesting the European Union would not be willing to renegotiate the deal currently on the table.
He told the audience: "The EU have just agreed on an orderly divorce with the UK.
"It is becoming more and more clear that this deal is the best possible, in fact, the only possible one.
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"If this deal is rejected in the Commons, we are left with an alternative, no-deal or no Brexit at all."
He added that the EU had "prepared for every scenario".
A Parliamentary vote on the deal will take place on December 11.
Around 18 Conservative MPs have publicly said they will vote against the deal, with a further 42 Conservative MPs adding that they are not in favour of it.