Three Conservative MPs have resigned, saying the party's "failure" to stand up to hardline Brexiteers has forced them to take the decision.
Sarah Wollaston, Heidi Allen and Anna Soubry have joined the new Independent Group.
In a joint letter to Prime Minister Theresa May, the MPs said: "We no longer feel we can remain in the party of a Government whose policies and priorities are so firmly in the grip of the ERG and DUP."
It comes hours after Labour MP Joan Ryan became the eighth MP from the party to resign and join the Independent Group.
The move takes the number of Independent Group MPs to 11.

Swiss police arrest suspect after deadly rave shooting
US strikes Iranian launchers on Larak Island
India must uphold water-sharing treaty with Pakistan, international court says
Nepal teams seek hundreds trapped in hydropower tunnels after deadly floods
