Tim Farron says Article 50 can be revoked
Liberal Democrat leader Tim Farron says he believes the formal procedure for triggering Brexit is reversible.
Speaking after meeting the European Parliament's chief negotiator, Mr Farron said notification under Article 50 of the Lisbon Treaty could be revoked "if there is the political will".
Article 50 begins two years of formal negotiations between the UK and the EU.
Prime Minister Theresa May has said she will do this by the end of March.
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Article 50 is the subject of the legal battle currently being played out in the Supreme Court between campaigners who say Parliament must authorise notification, and the government, which says it does not need to be consulted.
Both sides in the case say the process cannot be reversed - but some lawyers, and the peer who wrote Article 50, disagree.
After meeting Guy Verhofstadt in Brussels, Mr Farron said: "We discussed whether Article 50 can be revoked, and my conclusion is that if there is the political will, it would be possible to do so."
He added that Britons "deserve more than a deal imposed on them by Westminster or Brussels".
In theory the Supreme Court could refer the question of whether Article 50 can be revoked to the European Court of Justice for a ruling - but this is seen as unlikely as the question has not formed part of either side's arguments.
The Lib Dems are calling for a second referendum to be held, once negotiations are complete, on the terms of Brexit.
The government has refused to offer a "running commentary" on what it wants to secure from the talks.
Speaking to reporters in Brussels, Mr Verhofstadt warned that there would be "no flexibility" from the EU on freedom of movement rights if the UK wanted to retain the benefits of single market membership.
"We shall not compromise on that, that is very clear," he said.
Mr Verhofstadt also poked fun at the prime minister's goal of a "red, white and blue" Brexit, pointing out they were "the French colours".