The outcome of Brexit negotiations is “up to the UK”, European Council president Donald Tusk has said.
He told the European Parliament the UK would determine whether there was a “good deal, no deal or no Brexit”.
In an update following last week’s EU summit, the former Polish prime minister who represents EU leaders said he was “obsessed” with the remaining 27 countries in the EU staying united.
The UK’s departure, he added, was the EU’s “toughest stress test”.
“If we fail then the negotiations will end in our defeat,” he told MEPs. “It’s up to London how this will end: with a good deal, no deal or no Brexit.”
“But in each of these scenarios we will protect our common interest by being together.”
European Commission President Jean-Claude Juncker and the EU’s chief negotiator Michel Barnier are also addressing the Parliament.
On Monday, Theresa May told MPs she had a “degree of confidence” of making enough progress by December to begin trade talks.
Mr Juncker has dismissed a German newspaper’s account of his dinner with the PM in the run-up to the summit, which suggested Mrs May “begged for help” when they met and seemed tired and politically weak.
Speaking in Tuesday’s debate, Conservative MEP Syed Kamall, who heads the European Conservatives and Reformists Group, called for more pragmatism and less idealism from the EU in their approach to the talks.
The rest of Europe, he said, must recognise that the UK’s “main motivation” in building a future relationship of equals was maintaining open trade.
“There needs to be an understanding from the EU 27 where the British people are coming from,” he said.
“Perhaps the more the EU talks about the issues which resonate with the UK, it may find the UK is more willing to give concessions on the issues the EU 27 care most about and prioritise.”
Gabriele Zimmer, a German MEP who heads the European United Left group, said she did not want the British people to “pay the price of a no deal”.
She urged EU leaders to explain what criteria would be used to determine whether “sufficient progress” had been made to move onto trade discussions or whether it was a question of “political discretion”.