Mr Johnson insisted he was not seeking a no-deal Brexit but warned his party that it would face “mortal retribution” if the UK does not leave the EU by 31 October. And he claimed he could unite a divided country but made no specific mention of Scotland or plans to strengthen the Union.

He said: “I think it will be very difficult for friends in Parliament to obstruct the will of the people and simply to block Brexit.

“I think if we now block it, collectively as parliamentarians we will reap the whirlwind and we will face mortal retribution from the electorate.” He insisted he wanted a “sensible, orderly” departure from the EU but said the country had to prepare “vigorously and seriously” for a no-deal Brexit.

Boris Johnson during the launch of his campaign to become leader of the Conservative Party and Prime Minister. Picture: Stefan Rousseau/PA Wire

“The best way to avoid that is to prepare for it and be absolutely clear to our friends and partners that we are prepared to do that,” he said.

He warned that failure to deliver on the referendum result would create an “existential threat” for both Labour and the Conservatives.

“Around the country there is a mood of disillusion, even despair, at our inability to get things done,” Mr Johnson said.

“After three years and two missed deadlines we must leave the EU on October 31.”

His comments were seized upon by Mr Hammond, who said it would be “very difficult or impossible” to leave the EU by that date.

“I don’t think it’s sensible for candidates to box themselves into a corner on this,” he said.

“I think it will be very difficult - in fact I think it will be impossible - to do this by October 31 and I don’t think it will be in our national interest that we drive towards this cliff-edge at speed.”

The former Foreign Secretary’s momentum appears unstoppable, with dozens of MPs from both sides of the Brexit divide turning out to cheer him on. The first ballot of Tory MPs that will begin narrowing the field of ten candidates takes place today, with 81 of the Tory group in the House of Commons declared as backing Mr Johnson.

As he made his pitch for the party leadership yesterday, Mr Johnson said he represents “sensible, moderate, modern Conservatism”, despite courting fresh controversy by defending past comments - including comparing veiled Muslim women to letterboxes.

Mr Johnson also declined to clarify his past illegal drug use at his campaign launch event yesterday, which saw journalists jeered by his supporters.

He drew extensively on his experience as Mayor of London rather than referring to his controversial tenure as Foreign Secretary, arguing that strikes and riots in the capital meant he has “experience of managing real short-term difficulties in the confident expectation of long-term success”.

While Michael Gove has faced calls to quit the race over an admission of past cocaine use, and other candidates have revealed their histories with illegal substances including cocaine and opium, Mr Johnson appeared to side-step the issue when challenged by journalists.

The front-runner to become the next Prime Minister has been accused by rivals of “hiding in a bunker” because he has only faced media questions once this year, and took just six questions from reporters.

Mr Johnson said he “cannot swear that I have always observed a top speed limit, in this country, of 70mph” when asked whether he had ever done anything illegal.

Sky News political editor Beth Rigby was booed and jeered by supporters of Mr Johnson, including some MPs in the audience, as she asked about a newspaper column in which he wrote that “it is absolutely ridiculous that people should choose to go around looking like letter boxes”.

Mr Johnson said that “of course I’m sorry for the offence that I have caused”. But he went on: “Occasionally some plaster comes off the ceiling as a result of a phrase I may have used, or as a result of the way that phrase has been wrenched out of context and interpreted by those who wish for reasons of their own to caricature my views.

“But I think it’s vital that we as politicians remember that one of the reasons why the public feels alienated now from us all as a breed, is because too often they feel we are muffling and veiling our language, not speaking as we find - covering everything up in bureaucratic platitudes, when what they want to hear is what we really think.”

At least one candidate in the Tory leadership race will see their campaign come to an end today. Candidates need at least 17 votes to go through to the second round.

Even if all the hopefuls meet this target, the one with the lowest votes overall will be eliminated. The result of the first ballot is due at 1pm. A second ballot takes place on 18 June, when candidates will need at least 33 votes to go through.

Ballots continue until just two candidates remain in the contest, with a third scheduled for 19 June and a fourth and fifth on 20 June if necessary. The two candidates left at the end of the ballots will then spend a month campaigning across the country.

Conservative Party members will receive ballot papers through the post. The winner will be announced in the week beginning Monday 22 July.

Four TV debates have been scheduled, with Channel 4 inviting all remaining candidates on 16 June and the BBC doing the same on 18 June. The final two candidates will face off in July on the BBC and Sky News, with the dates to be determined.

Boris Johnson accused of driving UK to no-deal Brexit cliff edge