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Women MPs are being targeted with vile abuse by hardline Brexit backers infiltrating the Conservative Party, the Evening Standard can reveal.

Abuse including “mad bint”, “witch” and “mentally ill” has been used by Brexiteers backing a campaign to join the Tories in order to change the party’s leadership and direction.

The disclosure heaps pressure on party chairman Brandon Lewis to launch a probe into the motives of those who joined the party during a membership drive this summer.

New members have branded the Prime Minister a “traitor” and attacked ex-ministers Nicky Morgan and Dominic Grieve.

Prominent Remain campaigner Anna Soubry has been called a “gold-plated dope”, “sour-faced”, and a “tart” who should be “demoted to a whinging tea lady”. In a chilling Facebook post one man wrote: “Anna, we are coming for you”.

Other posts were by people who openly identified themselves as Ukip supporters who had joined the Tory party in recent months specifically to vote for a Brexiteer as its next leader.

Ms Soubry, who has been Parliament’s most vociferous supporter of Britain remaining in the EU, said the language being used against women should concern both Mr Lewis and Theresa May, as a “Tory woman Prime Minister”.

She said: “It is highly offensive. Some of the comments are exceptionally unpleasant. These people do not belong in the Conservative Party. A lot of these people are from the so-called far-Right. They are anti-women, anti-immigrant, anti-EU.

“Brandon Lewis needs to see what is happening to the party he chairs. Otherwise his legacy and Theresa May’s legacy will be a party that looks like Ukip-lite.”

A Conservative spokesman today said the comments uncovered by the Standard were unacceptable.

The party has sought to play down the threat of so-called entryism from those who want to pressure the party into backing a hard-Brexit and ousting Mr May in favour of Boris Johnson or Jacob Rees-Mogg.

MPs such as Robert Halfon, whose Harlow Conservative Association has seen a 24 per cent increase in membership, said new recruits should be welcomed.

However, the Standard spoke to a number of Tory MPs who admitted that over the summer the memberships of local parties have increased by double figures. One in a South East constituency said membership had increased by about 30 members this summer. Another in the North said they had seen 20 to 30 people join.

One Remain-backing MP said their membership has increased over the summer by double figures to over 200, and from meetings with their association executive they know that some people who have joined are hard-Brexit entryists. They said: “I’m keeping an eye on it. We need members from all sides of the Conservative party to join.”

Ms Soubry added: “If you get 25 new members that believe in hard-Brexit that 25 can be hugely influential because it means they will try to get on the executive, then there will be a letter condemning the Prime Minister ... that is what entryism is all about. Those people are fanatics and will go to all the meetings that are held.”

Writing on Leave.EU’s Facebook page about Ms Soubry, Kerry Rowe said: “I joined in February, knowing all too well you have to be a member for three months to be able to vote the final two! Once May is out I won’t be rejoining, I’ll be going back to Ukip.”

George Evans wrote on Twitter: “I voted Tory all my life. Joined Ukip to get the ref and Brexit. Left Ukip after the Brexit ref result and have now become a Tory member to see Brexit through. There’s nothing to fear from Brexiteers joining the party.” Others joining the party are life-long Conservative voters who are unhappy at the direction of the party. Roy Cox, 69, a businessman from Leave-voting Brentwood in Essex, told the Standard that he had joined after he “lost confidence” in the Prime Minister to negotiate Britain’s EU exit.

Brexit campaigner Arron Banks, who runs the Leave.EU campaign group, has called on supporters to join the Tories to influence a future leadership vote and lobby for a hard-Brexit.

One Tory MP said entryists have failed to realise Tory party rules and that 48 letters of no confidence in Mrs May need to be handed by Tory MPs to the chairman of the 1922 Committee of backbenchers, Graham Brady.

They said: “There are a lot of people joining. They are hard-Brexiters and they have joined up thinking there’s going to be a leadership election. They aren’t even close to getting the 48 letters in to challenge Theresa May. Also, even if there was a challenge, you wouldn’t get a new leader until December and the EU deal is done in November.”

A Conservative spokesman said: “Language of this kind has no place in politics or in today’s society and we have introduced a code of conduct that ensures complaints are looked into without prejudice.”