Lib Dem leader Jo Swinson says she hopes to convince members to back a policy of scrapping Brexit without another referendum, as the party’s conference begins in Bournemouth.
Ms Swinson says holding the referendum got the UK “into a mess”.
And she believes revoking Article 50 – the formal process to leave the EU – is the only satisfactory way out.
Ms Swinson said the party’s anti-Brexit message should be “unequivocal” in a general election campaign.
She told the BBC: “The Liberal Democrats are crystal clear. We want to stop Brexit… If a Liberal Democrat majority government is elected, then we should revoke Article 50 and I think it’s about being straightforward and honest with the British public about that.”
Up until now, the party’s policy on Brexit has been to campaign for another referendum – in which it would again call for the UK to stay in the EU.
But if Lib Dem members vote to back their leader’s policy proposal on Sunday, revoking Article 50 would be written into the next election manifesto.
Speaking on BBC Radio 4’s Today programme, Lib Dem deputy leader Ed Davey said a referendum would have been the best way to solve the problem, but “people want an end to this, and the only way you can stop Brexit in a democratic exercise like a general election is to say you would revoke”.
Meanwhile, amid reports that a new version of Theresa May’s Brexit deal could be supported by MPs, former Lib Dem leader Sir Vince Cable said the party would insist that it be put to a referendum, with an option to remain in the EU.
In an interview with the Guardian, Ms Swinson ruled out any kind of coalition with the Conservatives or Labour.
She said neither Conservative leader Boris Johnson nor Labour’s Jeremy Corbyn were fit to be prime minister.
Mr Johnson did not care about anyone but himself, she said, and she criticised Mr Corbyn’s failure to tackle anti-Semitism in his own party.
Parliament has so far denied Prime Minister Boris Johnson’s request for an autumn election, because opposition parties wanted to first make sure a bill designed to avoid a no-deal Brexit became law.
But since the bill, which seeks to force Mr Johnson to ask for a extension to the deadline, has been given Royal Assent, opposition MPs are preparing to start their general election campaigns.
Revoking Article 50 would effectively undo the legal mechanism under the EU’s Lisbon Treaty that was triggered to start Britain’s withdrawal from the European Union. Lord John Kerr, the British diplomat who was involved in drafting Article 50, has publicly said the clause is reversible.
Lord Ashdown tribute
Lib Dem environment spokeswoman Wera Hobhouse, who was one of the first delegates to address delegates at the Bournemouth International Centre, criticised the government’s record on the climate.
She said while the Tories had committed the UK to net-zero emissions by 2050, its policy on fracking was “madness” and they were action like “climate change deniers” with a reported plan to cut fuel duty.
Ms Swinson is expected to take questions from delegates on Sunday, following a speech by her predecessor Sir Vince Cable. It is likely to be Mr Cable’s last conference as a Lib Dem MP as he has said he will not contest his Twickenham seat at the next election.
Ms Swinson’s main speech will be held on Tuesday, the last day of the conference, after a tribute to the party’s former leader, Paddy Ashdown, who died in December.
Chuka Umunna, the former Labour MP who joined the Lib Dems three months ago, will speak on Monday in his role as foreign affairs spokesman.
The Lib Dems are enjoying a resurgence on the back of its anti-Brexit stance. The party currently has 17 MPs, having been boosted by a victory in the Brecon and Radnorshire by-election and defections from both Labour and the Conservatives over the summer.