The EU will be "defeated" in Brexit negotiations unless it maintains absolute unity, European Council president Donald Tusk has said.

The ex-Polish prime minister told the European Parliament the UK's departure was the EU's "toughest stress test" and it must not be divided at any costs.

"If we fail it then the negotiations will end in our defeat," he told MEPs.

But one German MEP said the EU's stance was "illogical, dangerous and unfair" and UKIP accused the EU of "extortion".