But former Tory minister Robert Halfon described her claim as “bonkers”. He said her view amounted to saying that “if any of the 17 million who voted for Brexit join the Tories that is somehow infiltration.
“If the Soubrites are so worried and have so much support then let them get hundreds of activists who have their point of view to join. I wouldn’t mind, the more members the merrier.”
And senior Tory MP Jacob Rees-Mogg pointed out that it is believed Ms Soubry had once belonged to the SDP, before it merged with the Liberals to form the EU-backing Lib Dems.
Defending the surge in membership from former Ukip members, he said: “The Tory party has often welcomed converts from other parties, even one or two who flirted with or even joined the SDP. This is not infiltration but the normal flow of political opinion.”
Former Ukip candidate George Eustice is a Tory MP and fishing minister.
In her outburst, former minister Ms Soubry said Tory party chairman Brandon Lewis needed to act.
She claimed that as part of a membership drive “the likes of” former Ukip backer Arron Banks are urging members and other Brexiteers to join the Conservatives to topple Theresa May as leader and destroy Government policy.
She said: “I’ve called on the party chairman to end the membership drive until we can be confident we are not being infiltrated.”
The original claims came from former justice minister Phillip Lee after the Daily Express revealed that most of the Ukip members in Dagenham had switched to the Conservatives.
Peter Harris, the former Ukip candidate and London organiser, told this newspaper that joining the Conservatives was the best way to ensure Brexit.
He said: “I no longer believe Ukip is the way to achieve that and I now believe that joining the Conservative Party and like-minded people within it we will be able to achieve more because after all the Conservative Party are in Government.”
Another Tory MP said: “We seem to have allowed a lot of people to join up who used to be in Left-wing parties. Chris Grayling and Greg Clark were in the SDP and Liz Truss was a Lib Dem.
“Perhaps it doesn’t matter if you’ve previously been in a Left-wing party.”
Mr Banks, blocked from joining the Tories this month, said yesterday: “I was a Tory member and donor up until 2013 – I left over the referendum. For the party chairman Brandon Lewis to pick and choose members they like seems a dangerous path.”
A leaked memo from Tory HQ yesterday revealed local organisers have been put on alert to scrutinise potential new members.