British Prime Minister Theresa May and her embattled Brexit plans face a fresh crisis after three of her own MPs dramatically resigned to join the exodus to a new independent party.

Leading pro-EU MPs Anna Soubry, Sarah Wollaston and Heidi Allen wrote a joint letter to Ms May on Wednesday night to confirm their departure before holding a media conference, criticising the government for letting the “hard-line anti-EU awkward squad” take over the party.

Their defection to the new Independent Group follows the resignation of seven Labour MPs on Monday over their party’s Brexit stance. They were joined by another former Labour MP early Wednesday, with more to follow suit in the coming days.

Ms May said she was “saddened” by the Conservative resignations, but vowed to stick to her controversial Brexit plans as she travels to Europe to plead for concessions ahead of the March 29 departure. 

“I am saddened by this decision. These are people who have given dedicated service to our party over many years, and I thank them for it,” the Prime Minister said in the statement.

“Of course, the UK’s membership of the EU has been a source of disagreement both in our party and our country for a long time,” she said, adding, “ending that membership after four decades was never going to be easy.” 

The resignations put Ms May in an even weaker position in Parliament, where her Brexit deal was crushed by MPs last month when eurosceptics and EU supporters voted against an agreement that both sides say offers the worst of all worlds.

They could also undermine Ms May’s negotiating position in Brussels, where she traveled to on Thursday morning for talks with Commission President Jean-Claude Juncker to try to secure an opening for further technical work on revising the agreement.

With only 37 days until Britain leaves the EU, its biggest foreign and trade policy shift in more than 40 years, divisions over Brexit are redrawing the political landscape. The resignations threaten a decades-old two-party system.

“The final straw for us has been this government’s disastrous handling of Brexit,” MPs Ms Soubry and Ms Wollaston said in a statement.

“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,” they said, referring to a group of Conservative pro-Brexit MPs and the Northern Irish Democratic Unionist Party that props up the government in parliament.

For Ms May’s Brexit plan, the resignations are yet another blow to more than two years of talks to leave the EU, which have been punctuated by defeats in parliament, rows over policy and a confidence vote, which she ultimately won.

-with AAP