Boris Johnson has dismissed warnings by senior ministers that Parliament will find a way to block a no-deal Brexit as a "red herring", as he condemned the "defeatism and negativity" in Government about the prospect of leaving the EU.
The Tory leadership frontrunner told the party faithful at a hustings in Darlington that the Conservatives were languishing in the polls because "MPs seem still to be refusing to enact the mandate of the people".
His comments came after Chancellor Philip Hammond, Justice Secretary David Gauke and ex-minister Sam Gyimah said MPs would not allow Britain to leave the EU without an agreement with Brussels.
Mr Johnson said: "I think this is all a bit of a red herring. We are facing an existential crisis as a party and indeed as a political class.
"It was a clear, clear majority for Leave. Now we are at a state where MPs seem still to be refusing to enact the mandate of the people. That is why our great party is languishing in the polls.
"If we get on and do Brexit we will spike the guns of both the Liberal Democrats and the Brexit Party who are prospering at our expense because of our failure to get this done.
"I hope that Philip and Sam and all the other friends that you mentioned can see that."
Mr Hammond told the BBC it would be "shocking" if the next prime minister tried to sideline Parliament to push through a no-deal Brexit, and that he was confident MPs would find a way to block such an attempt.
Elsewhere, Mr Gauke told Parliament's The House magazine: "If I was to speculate on it, given that we have an activist Speaker, given that there is a parliamentary majority against no-deal, a way will be found."
He was backed by former minister Sam Gyimah, who said some Tory MPs would even vote for a no-confidence motion to bring down the Government to prevent no-deal.
Mr Johnson condemned what he said was the "defeatism and negativity" in Government about the prospect of Brexit, saying his message was that "we have to get ready, we have to prepare and we have to believe in ourselves".
"The reason I have set October 31 as a hard deadline and we have got to go for it is that we have had enough of defeatism and negativity from this Government.
"People have had enough of being told they can't do X, Y or Z when we know perfectly well that we can."
His rival Jeremy Hunt, the Foreign Secretary, called on all sides to "dial down the rhetoric" in the debate on Brexit.
He dismissed comments by the Brexit Party MEP Ann Widdecombe likening Brexit to the emancipation of the slaves.
"Ann Widdecombe is not in the British Government, she is not even in the Conservative Party," he said.
He added: "I think there has been some terrible rhetoric on the EU side about the United Kingdom which has been the biggest friend to the European Union the whole time we have been in it, which has defended Europe with our armed forces.
"So I think we have to dial down the rhetoric on all sides and come to a sensible way forward that allows us to leave the European Union cleanly and also be the best of friends afterwards."
Mr Hunt is pledging to set out his plans to overhaul the social care system within 100 days of entering No 10 if he wins the leadership race.
The former health secretary said he regarded reform of the adult social care system as "unfinished business".
He said he would publish his proposals – including incentives to encourage people to save for their care needs in the way they do for pensions – in a Green Paper.
His promise came after a House of Lords committee warned that it would need £8 billion a year to fix the underfunding in the system.
Meanwhile, Mr Johnson said he will make Britain "the greatest place on Earth" if he succeeds in gaining the keys to 10 Downing Street.
With some party members already reportedly having received their postal ballot papers – two days earlier than previously expected – Mr Johnson said he was "fighting for every vote".
"I'm taking nothing for granted," the former foreign secretary – seen as the clear front-runner – told the Daily Telegraph.
"It's time to drive for the line, keeping the ball at the back of the scrum. I'm fighting for every vote and campaigning flat out and will be from now until the end."