Six MPs have quit the Change UK party, with high-profile figures including Chuka Umunna and Heidi Allen walking out of the newly formed party.
Anna Soubry has become leader and criticised her fellow MPs, telling them "now is not the time to walk away."
The split comes after the party, originally called the Independent Group, performed badly in the European Parliament elections, securing just 3.4% of the vote.
The party was formed in February by MPs who rejected the main political parties' stance on Brexit and other issues and defected from the Labour and Conservative party.
Ms Allen had been the party's leader and My Umunna was spokesman, but they left the party on Tuesday, along with Luciana Berger, Gavin Shuker, Angela Smith, and Sarah Wollaston.
Along with former Tory minister Ms Soubry, the remaining Change UK MPs are Chris Leslie, Joan Ryan, Mike Gapes and Ann Coffey.
Ms Soubry said: "I'm deeply disappointed that at such a crucial time in British politics our former colleagues have made this decision.
"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 Change UK MPs are "determined to fix Britain's broken politics" and admitted challenging the main poltical parties "was never going to be easy."
"We registered as a political party to stand in the European elections but it was never our sole purpose," Ms Soubry said.
"It is vital we continue leading the fight against a damaging Brexit, pressing for a People's Vote and being prepared to revoke Article 50 in the face of a no-deal Brexit."
A joint statement issued by the outgoing Change UK MPs said: "We are very grateful to everyone who has supported us over the past four months since we left our respective political parties.
"Heidi Allen, Luciana Berger, Gavin Shuker, Angela Smith, Chuka Umunna and Sarah Wollaston have made the decision to leave Change UK, returning to supporting each other as an independent grouping of MPs.
"We believe that our priority right now must be to provide collegiate leadership to bring people together in the national interest.
"We know the landscape will continue to shift within the political environment and have concluded that by returning to sit as independents, we will be best placed to work cross party and respond flexibly."