The EU has insisted repeatedly that it will not renegotiate the terms of the divorce, while parliament has previously voted against leaving without an accord.
Brexiteers such as Dominic Raab and Esther McVey have said the priority must be honouring the 2016 referendum result and the United Kingdom should be prepared to accept no deal.
To a packed room where some supportive politicians were forced to stand, Mr Johnson drew on his past as a former London mayor to try to persuade Conservatives that only he could take the party to election victory, explaining away some of his well-documented gaffes as his desire to "speak as directly as I can".More news: Saudi Arabia, Russia work to prevent oil prices dip: minister
He acknowledged that his use of language - such as his description of Muslim women who wore the burka as letter boxes - sometimes resulted in "some plaster coming off the ceiling".
However, he refused to clarify whether he had taken cocaine, an issue that has dogged leadership rival Michael Gove.
"Instead, we have witnessed candidates openly advocating a damaging no-deal Brexit and even proposing dragging the Queen into politics by asking her to shut down Parliament to achieve this".
Johnson added: "I think it is right for our great country to prepare".
This would mean, the European Union statement said, there would be no transition period next year - which officials estimate would save Britain around 12 billion euros on the bill - but the balance would be outstanding. "If he continues like this he will lose the trust of his MPs, he will lose the trust of the members of the Conservative Party, and ultimately the trust of the electorate".More news: Horrifying footage shows helicopter moments before it crashes into NYC skyscraper
"If such a bill were to pass, the tensions within Parliament would likely escalate towards a general election".
Johnson's supporters believe he is the only leader who can win against the twin threats of leftist Labour leader Jeremy Corbyn and eurosceptic Nigel Farage.
Conservative frontrunner Boris Johnson warned that MPs face "mortal retribution" if they fail to deliver Brexit.
MPs voted 309 to 298 against the measure which would have enabled politicians to size control of the House of Commons later this month.
"We didn't and we are not", said Mr Varadkar, speaking in the Dáil (Irish parliament) on Tuesday.More news: Scientists predict 'very large dead zone' in Gulf of Mexico