They are said to join up with the Independent Group, raising its member tally to 11, 1 more than the DUP.

In their joint resignation letter, the trio said: “We had hoped you would also continue to modernize our party so that it could reach out and broaden its appeal to younger voters and to embrace and reflect the diversity of the communities we seek to represent. 

"Sadly the Conservative Party has increasingly abandoned these principles and values with a shift to the right of British politics. 

"We no longer feel we can remain in the party of a Government whose politicize and priorities are so firmly in the grip of the ERG and DUP".

Theresa May has said she is "saddened" by the decision of Heidi Allen, Sarah Wollaston and Anna Soubry to leave her party.

"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.

"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. Ending that membership after four decades was never going to be easy.

"But by delivering on our manifesto commitment and implementing the decision of the British people we are doing the right thing for our country. And in doing so, we can move forward together towards a brighter future.

"I am determined that under my leadership the Conservative Party will always offer the decent, moderate and patriotic politics that the people of this country deserve."