They amount to an implicit rebuke to Jeremy Corbyn, who is coming under growing pressure from the Labour rank and file to adopt a tougher anti-Brexit stance.

More than 60 local Labour Party branches have backed a move to force Mr Corbyn to fully oppose Brexit, paving the way for a major battle at the party's annual conference later this month.

New Lib Dem leader Jo Swinson proposed the revocation policy in one of her first major initiatives after taking office in July, and it is expected to be endorsed by the party this weekend.

While the Lib Dems remain committed to a Final Say vote on any EU deal, they will fight any general election taking place before a referendum on a platform of withdrawing the letter - sent by Theresa May in March 2017 - notifying Brussels of the UK's intention to leave under the Article 50 process.

The move makes all but impossible an election "Remain alliance" with Mr Corbyn's party, which backs a referendum but is expected to fight on a manifesto promise to put credible Remain and Leave options to voters.

Speaking ahead of his appearance at a rally to kick off the Bournemouth gathering, Mr Verhofstadt said: "As the European Court of Justice has determined, a decision to revoke would unilaterally end the Brexit process.

"This is the only way to stop Brexit, given that Article 50 has been triggered.

"It is a natural stance for a party committed to stopping Brexit to take."

Mr Verhofstadt, a former Liberal prime minister of Belgium who was the target of Brexiteer fury after a fly-on-the-wall TV documentary aired footage of him and his staff disparaging Ms May and her negotiators earlier this year, said that there was "deep concern" on the continent about the chaotic state of the Brexit process.

"Right across Europe, people are deeply concerned about the damage caused by this chaotic Brexit process," he said.

"Businesses and our citizens need certainty and this will only be achieved by a positive decision in favour of something."

Anti-Brexit campaigners said some 61 Labour Party branches have voted to submit a motion to the party's conference in Brighton calling for a stronger pro-Remain stance. The actual figure could be higher when Labour releases official totals next week.

Most of the motions submitted are based on a template saying Labour should "campaign energetically for a public vote and to Remain" and "support revoking Article 50 if necessary to prevent no deal". They say the party should also "defend free movement and extend migrants' rights".

It raises the prospect of a fresh battle between activists and the party leadership when the motion is debated by delegates at the gathering. The text is likely to be amended during lengthy discussions to hammer out a compromise, with Mr Corbyn's team and some trade unions expected to try to tone down some of the more anti-Brexit language.

Michael Chessum, national organiser for Another Europe is Possible, said: "In an election, Labour needs the space to articulate a radical set of policies that will transform the economy and people's lives. In government, it needs to be able to deliver on its promises. To have either of these things, we need to defeat Brexit and move the conversation on.

"The public wants this to be over - any sense that we are going to engage in a lengthy renegotiation will be deeply unpopular. In government, Brexit would be an albatross around our necks - a pointless loss of time and energy, probably a loss of rights and protections and a fracturing of our support base."

Labour MP Clive Lewis, a supporter of the campaign, said: "As an MP, I know what wins elections for Labour - it's our members, who are more than 90 per cent in favour of Remain.

"Our army of volunteers aren't just foot soldiers, they're members of a democratic movement. They need to feel ownership over our Brexit policy, they need to be excited and enthused by it. Yes, the people should have the final say, but for our morale we need a clear anti-Brexit position in Labour. That means we must campaign in any public vote for Remain."