Change UK, the fledging party formed by ex-Tory and Labour MPs, has split after just four months.
Eleven MPs came together in February to form what was originally known as The Independent Group, before adopting the name Change UK for the European elections.
Read more: Change UK has no hope among voters
The party, which opposed Brexit and supported another EU referendum, polled just 3.3% in last month’s European Elections – with the Lib Dems enjoying a resurgence as the most popular ‘Remain’ party.
The party was divided over whether to form an electoral alliance with the Lib Dems, with interim leader Heidi Allen backing the move, while her former Tory MP Anna Soubry was opposed.
On Tuesday afternoon it was announced that six MPs – Allen, Chuka Umunna, Luciana Berger, Gavin Shuker, Angela Smith and Sarah Wollaston – all quit the party.
In a statement, Soubry – who is now the leader of the now five-strong group – 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.”
The six MPs who quit Change UK released a joint statement saying they will return to “supporting each other as an independent grouping of MPs”.