Tory rebel Michael Heseltine has launched a scathing attack on the Prime Minister’s handling of Brexit and accused her of leaving many party members feeling "appalled and betrayed".
And Lord Heseltine - who was last week sacked as a Government adviser for rebelling over Brexit - insisted he will stay in his party "and fight".
Speaking to ITV's Peston on Sunday, he said Zac Goldsmith's defeat in the Richmond by-election last year is far more significant than the Conservative Party's "fluky" win in Copeland, where Labour suffered an historic defeat.
He said: "My postbag is from that very, very large minority - almost half - many of whom are bitterly disappointed with the Tory Party.
"You shouldn't be talking about a fluky by-election on the nuclear industry in the north of England, you should be talking about Richmond. See what happened there, where Europe was the central issue.
"And the fact is that a huge number of Conservatives are appalled, they feel they have been betrayed by what is going on now.
"Those of us in politics, those who care, we are not performing fleas where the ringmaster says 'jump' and we all turn hands up over ourselves. We are not like that.
"We happen to believe, for all sorts of very powerful reasons, that British self-interest was inextricably interwoven with those of our European allies."
Pressed on whether he would ever resign from the Tory Party, the former Cabinet minister said he will stay "and fight".
He told the show: "I remember this phrase I think - pick your party, damn your principles. Well I hope I don't damn my principles but I won't leave my party."
The Brexit Secretary David Davis had earlier revealed that the Government is drafting emergency contingency plans in case Britain crashes out of the European Union without a deal.
Mr Davis told BBC One's The Andrew Marr Show that he had briefed the Cabinet on contingency plans and that the country would be ready if the negotiations "go wrong”.
"The aim is to get a good outcome and I'm confident I'll get a good outcome.
"One of the reasons we don't talk about the contingency plan too much is we don't want people to think this is what we are trying to do."
But the Commons Foreign Affairs Committee said there was real possibility the talks could end with no deal and added it had seen no evidence of serious contingency planning by Government.
It said ministers should order all Whitehall departments to draw up a "no deal plan", warning that failure to prepare for such an outcome would be a "serious dereliction of duty".
Boris Johnson said it is "excessively pessimistic" of the select committee to suggest there is a real possibility Britain will tumble out of the EU with no deal and revert to World Trade Organisation rules.
But he said that if this did happen it would not be "apocalyptic" and the UK would continue to thrive.
Speaking on ITV's Peston on Sunday, the Foreign Secretary said a deal is a "very likely" outcome, stressing that the UK has a "robust" economy and a confident negotiating team.
"I think that actually, as it happens, we would be perfectly OK if we weren't able to get an agreement, but I'm sure that we will, for the reasons that I gave", he said.
"I don't think that the consequences of no deal are by any means as apocalyptic as some people like to pretend."