Six of Change UK’s 11 MPs, including its spokesman, Chuka Umunna, and interim leader Heidi Allen, have abandoned the fledgling party after its dire performance at the European elections.

Change UK announced that it now had just five MPs, who will be led by the former Conservative business minister and anti-Brexit campaigner Anna Soubry.

The others remaining are the former Labour MPs Mike Gapes, Chris Leslie, Joan Ryan and Ann Coffey. In their statement, they said they would embark on a “nationwide programme of deliberative democracy”, across the UK.

“Change UK doesn’t just belong to MPs. It belongs to the country and those looking for a sense of hope and leadership to genuinely change our politics,” the five said in a statement.

“We are in it for the long haul,” Leslie said. “It was never going to be easy to challenge the established parties. Of course there’s a whole treacle of cynicism that gets poured on people who try to do something different.”

He said the MPs had agreed that Soubry, who has been a leading figure in the People’s Vote campaign was “absolutely the clearest voice” in the “Brexit maelstrom” – and that they did not want to waste crucial weeks selecting a leader, like the Conservative party.

Soubry said she was “deeply disappointed” that colleagues had resigned. “Now is not the time to walk away, but instead to roll up our sleeves and stand up for the sensible mainstream centre ground which is unrepresented in British politics today,” she said.

Several of the MPs who have quit the party are believed to be considering defecting to the resurgent Liberal Democrats, although they issued a statement saying that they would initially sit as a group of independents.

Allen and Umunna have both been advocating closer cooperation with Vince Cable’s party. Some of their erstwhile colleagues suspect they may have been offered plum seats, or the backing of Lib Dem activists in their existing constituency, if they defect.

The other four MPs to quit the party were Luciana Berger, who fronted its slick press launch on London’s South Bank in February, Gavin Shuker, who had spent months drawing up secret plans for the breakaway group, Sarah Wollaston and Angela Smith.

Change UK, which was initially called the Independent Group, caused a stir in Westminster when it was launched four months ago after the defection of seven Labour MPs. It had hoped to become the catalyst for a major political realignment, attracting a string of other recruits and becoming the rallying point for remainers.

High-profile candidates including the former Conservative minister Stephen Dorrell, and the journalists Rachel Johnson and Gavin Esler, joined the party’s list of prospective MEPs.

However, it has been beset by internal disagreements over strategy and management, including how closely to cooperate with other parties.

Change UK’s leading candidate to become an MEP in Scotland, David MacDonald, stepped aside from the race and recommended voting for the Lib Dems. Two other candidates resigned after offensive social media posts were uncovered.

Even before the European election polling day, Johnson questioned its strategy, saying: “If I were running it, we would have one leader and a different name and we would have done a deal with all the other remain parties. Then we would be able to give the Brexit party a fight.”

Allen, the South Cambridgeshire MP, was appointed interim leader, but Umunna was still widely regarded as Change UK’s public face. Allen admitted she had considered resigning in the run-up to the European elections. She had suggested voting tactically for the Lib Dems in that poll, a proposal Soubry later called “rather bizarre”.

Soubry and Umunna had struck up a close political friendship as co-chairs of the cross-party group on EU relations, which coordinated the tabling of anti-Brexit amendments in parliament.

But the pair clashed over Change UK’s future direction, with Soubry determined that it should continue as a political party, while Umunna became convinced it could only survive by striking up a close alliance with the Lib Dems.

Cable’s party positioned themselves as the leading pro-remain party at the European elections, with a punchy “bollocks to Brexit” slogan. The party’s strong performance, scooping up 20% of the vote, followed gains in local elections in May. Change UK, in contrast, took 3%.

Umunna published a statement on his website on Tuesday, saying he had differed with colleagues over the party’s direction.

“While I believe it should carry on as an organisation, I do not believe Change UK should carry on in its current form. This has put me in a fundamentally different place not only to other Change UK parliamentary colleagues but also its activists and candidates who should be free to take the party in the direction they wish,” he said.

He added that he planned to sit as an independent in parliament, “for the time being”.

With Cable stepping aside, frontrunners for the Lib Dem leadership, Ed Davey and Jo Swinson, have suggested they would welcome new recruits.

Swinson said: “As the European and local election results showed, the old, two-party politics is fracturing. The Liberal Democrats are at the heart of the fight against nationalism and populism and I want to lead this party to grow that movement.”

Davey, who had been more sceptical about the idea of an electoral pact with the breakaway group, said: “Change UK’s swift demise shows that my reluctance from the beginning to discuss mergers and pacts, and to hold firm in our belief that the Liberal Democrats are the clear home for all who want to stop Brexit, was the right call.”