Pro-EU Conservative MPs have reported a wave of new Brexiteer members joining the party.

They believe they are being deliberately targeted by UKIP activists in an attempt to overthrow both them and Theresa May.

Brexit funder Arron Banks has called for UKIP members to flood the Conservative party.

May suggests she would fight any any attempt to force her out in order to install Boris Johnson as prime minister.

LONDON — Pro-EU Conservative MPs believe the party is being deliberately infiltrated by UKIP activists as part of a plot to overthrow Theresa May and install a hardline Brexiteer leader as UK prime minister.

Conservative MPs Stephen Hammond, Dominic Grieve, Anna Soubry, Nicky Morgan and Sarah Wollaston have all reported a big influx of new members in recent weeks, with their local constituency membership growing by as much as 30%, according to the Times.

The influx follows a recent call by Brexit-backing financier Arron Banks for UKIP activists to flood the Conservatives in order to overthrow 'extreme Remain' MPs and replace May with a more hardline Brexit supporter such as Boris Johnson or Jacob Rees-Mogg.

One Conservative MP called for a freeze on new members in order to put a halt to the wave of entryists joining the party.

"We are on a membership drive at the same time as the likes of Banks are urging members of Ukip and other hard Brexiteers to join our party to topple the leader and destroy government policy," Anna Soubry told the paper.

"I’ve called on the party chairman to end the membership drive until we can be confident we are not being infiltrated by people who are not Conservatives."

Banks, who was one of the main funders of the campaign for Brexit, wrote this week that he was encouraging UKIP activists to target extreme ‘remain’ MPs within the Conservatives.

"The best way to secure Brexit and our country’s future is via the Conservative Party," he wrote.

"It is in government and, for now, calls the shots. To that end I am urging the 90,000 members of my Brexit campaign Leave.EU, and the 1.4m who follow us on social media, to join the Conservatives and have a say."

An application by Banks and his colleague Andy Wigmore to join the Conservatives was recently rejected by the party.

Asked during a visit to South Africa on Tuesday whether she would fight a leadership challenge against Johnson, Theresa May replied that "I’m in this for the long term."

Conservative supporters of Johnson have called for a change to party leadership rules which make it difficult for Johnson to get into the final two in any future leadership challenge.

Johnson remains very popular with members, but is highly divisive among Conservative MPs. Under party rules, MPs vote on which two potential candidates should be put before a final vote of members. Johnson's supporters want the rules changed to allow candidates with minority support among MPs to also make it through to the final ballot.