BORIS Johnson is driving Britain towards a cliff-edge Brexit at speed, Philip Hammond has warned, as the former Foreign Secretary called for “guts and courage” to deliver Britain’s withdrawal from the EU.

As Mr Johnson broke cover to launch his Tory leadership bid – ahead of today’s first vote to whittle down the 10 candidates - he took a sideways swipe at Theresa May, criticising her “astonishing” decision to remove the threat of a no-deal, which he described as a “vital tool of negotiation”.

While the Conservative frontrunner told a packed central London launch - bedecked by the slogan “Back Boris” - that he did not want a no-deal outcome, he insisted the country had nonetheless to prepare vigorously for one.

“It’s only if we have the guts and the courage to get ready for it that we will carry any conviction in Brussels and get the deal we need.

“Delay means defeat, delay means Corbyn; kick the can again and we kick the bucket,” declared Mr Johnson.

But the Chancellor, speaking at an economic summit in the City of London, said it was not sensible for Mr Johnson to box himself into a corner on Brexit.

He was adamant Parliament would not allow a no-deal exit and Brussels would not reopen the Withdrawal Agreement.

Mr Hammond added: "It will be very difficult - in fact 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.”

At his campaign launch, attended by dozens of MPs, Mr Johnson suggested he wanted to do for the country what he had done for London during his time as mayor: reduce crime, increase the pay of the less well-off and build affordable homes.

He spoke of narrowing the “opportunity gap,” promoting social justice and strengthening the Union, which he described as the “invincible quartet, the awesome foursome, the world’s soft power superpower”.

He claimed the Union flag represented economic and political freedom, democracy, free speech and human rights.

On Brexit, Mr Johnson insisted Britain had to leave on October 31 with or without a deal and he warned if MPs blocked Brexit, they would “reap the whirlwind” and face “mortal retribution”.

He said it was time for the country to unite but this could not happen until Parliament delivered on the “primary request of the people”.

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

The post-launch press conference saw the leading candidate dodge difficult questions about whether voters could trust him.

Asked about his previous confession that he had taken cocaine while at university, the former London Mayor replied: “The account of this event when I was 19 has appeared many, many times.

“What most people in this country want us to really focus on in this campaign, if I may say so, is what we can do for them and what our plans are for this great country of ours."

When he was asked about his controversial remarks about Muslim women looking like bank robbers and letterboxes and that those who worked with him did not believe he was fit to be PM, the questioner was met with vocal protests from supportive MPs.

To applause, Mr Johnson said he was delighted many of his colleagues appeared to dissent from the sentiment of the question.

He admitted that occasionally “some plaster comes off the ceiling” from a phrase he might have used or which might have been misinterpreted by his detractors.

“But it is vital 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 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 genuinely think. If sometimes in the course of trying to get across what I genuinely think, I use phrases and language that has caused offence, then, of course, I’m sorry for the offence that I have caused. But I will continue to speak as directly as I can.”