Britain’s EU exit should be stopped to allow time to hold a second referendum, according to Change UK.
Party spokesman Chuka Umunna said the country was facing a “national emergency” – the prospect of leaving the EU with no deal at the end of October.
“I have come to the view that we are now at the point where we are going to need to revoke Article 50,” he told the BBC’s Andrew Marr Show.
“The way to resolve this impasse is to refer it back to the people.
“The simple fact right now is we do not have time to do a People’s Vote [what some campaigners call a second referendum] before October 31.”
He added: “What would be undemocratic is to impose a no-deal Brexit on this country which there is not a mandate for.
“All the polls show the majority of people want to remain in the European Union.
“We are faced with a national emergency. No deal is facing us in the face now and we have got to deal with it.”
Article 50 is the legal mechanism for triggering a country’s exit from the EU.
Under the bloc’s rules, a country has two years to negotiate the terms of its departure and can request extensions if it wants to.
Appearing on Sky’s Sophy Ridge on Sunday, the party’s Brexit spokesperson Anna Soubry said revoking Article 50 was preferable to a no-deal divorce.
She said such a course would be the “stuff of economic madness”.
Ms Soubry said: “Revoke has got to be a realistic option and I would vote to revoke.
“For our country to leave without a deal would be a disgrace as it would not be in anybody’s interests in this country.”
Change UK – formerly known as The Independent Group – is made up of eight former Labour MPs and three ex-Tories who left their respective parties in February in a bid to establish a new force in British politics.
But Change UK is only polling around 3% ahead of Thursday’s European elections, with suggestions it may fail to gain a single MEP.
Despite this, Ms Soubry said the party is doing “remarkably well” and rejected suggestions it will be finished if it does not win any seats on Thursday.
“We are up against these big Goliaths and I think my big takeaway from all this, when I go to the rallies and am actually just out and about, I genuinely believe there is a real thirst in our country,” she said.
“Millions of people believe nobody represents them.
“They want that sensible, centrist, moderate but progressive politics, accepting that all the political parties are responsible for the breaking of politics and I believe, I genuinely believe we offer the change the people of this country are desperate to receive.”