A senior Tory MP has compared Conservative grassroots members to the Taliban and warned that MPs are afraid to speak out over Brexit due to fears of being deselected.
Dominic Grieve, the former attorney general, argued that there was Conservative support for a second referendum but some MPs were reluctant to act following confidence motions against several pro-EU Tories.
Speaking at an event in London, Mr Grieve said Boris Johnson had been "radicalised" over Brexit, leaving a Final Say referendum as the only credible option to thwart a disorderly exit from the EU in the autumn.
His comments came after Mr Johnson told a leadership hustings that the Irish backstop proposal was "dead" and vowed to scrap it from any Brexit deal.
Mr Grieve, who has led a string of Brexit rebellions, said there was a "substantial number" of Conservative MPs for whom "no-deal is completely unacceptable" but admitted that there was a lot of "can-kicking" underway.
He told a People's Vote event: "They do exist. They sometimes have concerns about their own local associations and the fear of being deselected, I think there is absolutely no doubt about that.
"There has been a sort of Talibanisation of sections of the Conservative Party grassroots membership, with some vociferous minorities that are often capable of dominating meetings coming along trying to get rid of MPs, interestingly enough, who have been totally loyal but simply have indicated by the occasional expression of doubt that the purity of the ERG Brexit vision might be mistaken.
"They have been at the rough end of quite a lot of difficulty and I think that's one of the reasons why they tend to hide a little behind the parapet."
Mr Grieve is among several pro-EU Tories who have faced confidence votes over Brexit from their local associations, including Philip Lee, Sam Gyimah and David Gauke.
He raised the prospect that he will resign the Tory whip in the likely event that Mr Johnson becomes prime minister next week over concerns about his suitability to lead.
Mr Johnson's bid to become prime minister looks all but assured, with the results of the ballot of Tory members expected next week.
Mr Grieve said the Tory frontrunner's pledge to scrap the backstop were an example of how the leadership race has been "played to a tune of growing extremism".
He said: "When challenged and confronted he radicalised even further and excluded any possibility of trying to negotiate some way out of the backstop at all. It had to go in its totality.
"The consequence of that is make it the choices starker and starker."
Ex-Labour foreign secretary Margaret Beckett told the event that she was not surprised by Mr Johnson's backstop comments, adding: "I've thought for weeks, months, if it came to it they would be prepared to throw the Irish situation under a bus.
"That they should however take that point of view I think is quite terrifying, considering what we know and what the problems in Ireland have been in the past."
Both MPs were speaking at the launch of a cross-party study that warned all other routes out of the Brexit crisis - such as a general election or renegotiating Theresa May's deal - were doomed to fail.
The next prime minister would then be forced to suspend parliament to force through a no-deal but would face an immediate confidence vote, the report argues.