The president of the European Council has suggested the UK could still decide to reverse Brexit.

Donald Tusk said negotiations could end in "no Brexit" if the British government wanted to.

"Ahead of us is still the toughest stress test. If we fail it, the negotiations will end in our defeat," he said in a speech at the European Parliament in Strasbourg.

"We must keep our unity regardless of the direction of the talks. The EU will be able to rise to every scenario as long as we are not divided."

"It is in fact 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 only by being together."

Legal opinion is split on whether Britain can unilaterally decide to revoke its triggering of "Article 50", the European Union treaty clause that sent the UK on its way out of the bloc.

If the clause is not revoked or no intervention is made to extend the withdrawal period with the unanimous consent of all 27 remaining member states, the UK will automatically leave without a deal in March 2019.

Brexit: the deciders Show all 8 1 /8 Brexit: the deciders Brexit: the deciders European Union's chief Brexit negotiator, Michel Barnier Getty Brexit: the deciders French President Emmanuel Macron Getty Brexit: the deciders German Chancellor Angela Merkel Reuters Brexit: the deciders Commission President Jean-Claude Juncker EPA Brexit: the deciders The European Parliament's chief Brexit negotiator Guy Verhofstadt Getty Brexit: the deciders Britain's Prime Minister Theresa May Getty Images Brexit: the deciders Britain's Chancellor of the Exchequer, Philip Hammond PA Brexit: the deciders After the first and second appointed Brexit secretaries resigned (David Davis and Dominic Raab respectively), Stephen Barclay is currently heading up the position PA

The UK would be unlikely to halt the Brexit process, however, because both the main parties say they will respect the result of the 2016 referendum that saw Britain vote to leave. The Liberal Democrats are calling for a referendum on the final deal.