Beth Rigby, political editor

"Do or die", the UK must leave the UK on 31 October. This is the sort of fighting talk Boris Johnson knows will rouse Brexit supporters to his cause.

His campaign got off to a shaky start after revelations over a late night row with his girlfriend, coupled with a distinctly lacklustre performance at the first hustings in Birmingham interviews. What better way to get on the front foot once more than brandishing your trump card as the true Brexit believer in this race.

Mr Johnson didn't want to debate with Jeremy Hunt face-to-face on Sky News, but he did send his rival a letter instead demanding he agree that the UK should leave the EU on Halloween "no matter what".

From the 31 October date being "eminently feasible" a week ago in the BBC TV debate to absolutely nailed on Tuesday, Mr Johnson is sharpening his message by trying to bounce Mr Hunt into signing up to his (and Nigel Farage's) hard deadline. Leaving on Halloween is now the "central question" of this leadership race, according to the Johnson camp.


Of course this is the laser-sharp focus of the Johnson campaign - what the former foreign secretary has over the current one is the fact he campaigned to leave the EU when his rival Mr Hunt did not.

What Tory activists and MPs - terrified by the prospect of a Brexit party annihilation - want to know above all else is that the UK will leave on 31 October. The political imperative to see off what Mr Johnson dubbed the "existential threat" to the party has trumped the Conservatives' pro-business instincts. To put it simply - perhaps even literally - the UK must leave the EU whatever the cost.

But its not the question of whether we leave on 31 October but a question of how we leave.

Image: Boris Johnson's pitch for Number 10 is based on being a true Brexit believer

Mr Johnson can say we are leaving on that date as many times as he likes, it doesn't make it true. Parliament - aided by the speaker John Bercow - could well try to block a no-deal exit by tabling legislation that either demands the prime minister ask for an extension - and it would be up to the EU27 to accept or reject that request, or revoke Article 50 and cancel Brexit altogether.

However it plays out in the autumn, the way it is playing out in the leadership contest right now is like a re-run of the Vote Leave campaign where people were being sold promises that just didn't stack up.

:: Listen to the All Out Politics podcast on Apple Podcasts, Google Podcasts, Spotify, Spreaker

Because instead of having an honest debate in this contest about whether or not the UK should move to no deal and what that might mean, the Johnson camp has muddied the waters by confecting a row about whether or not we can invoke an obscure clause in international trade law - Article XXIV of the General Agreement on Trade and Tariffs (GATT) - to leave without a deal while also agreeing a "standstill" tariff arrangement with the EU.

Countless trade lawyers have queued up to explain that this provision allows two parties to maintain preferential trading relationship while they finalise a trade deal. It is not an interim arrangement to ensure no tariffs in the event of a no deal, and the EU has been crystal clear that it will not even entertain this arrangement in the event of no deal.

But the very discussion of this no-deal tariff arrangement - however confected - leaves the impression that we could, somehow, leave in an orderly way without a deal.

It is rather - as my colleague Ed Conway pointed out this week - like the £350m claim on the side of that Vote Leave bus.

While the media and politicians rowed over whether this was a fair number (it was a gross contribution so didn't account for the amount we got back from the EU in various other forms such as farm subsidies), the Vote Leave team got the idea of an NHS bung - however big or small - into the consciousness of voters.

And in a similar way three years on, Mr Johnson is using this notion of a tariff-free no-deal Brexit as a neat way of avoiding a conversation about what sort of tariffs will hit farmers or car makers in the event of no deal.

As long as Team Johnson keeps the idea alive, they can duck questions on the serious economic risks, while also paving the way to blame a disorderly Brexit on the EU when they rule out this option in a few weeks time.

We desperately need an honest debate on whether the trade off of coming out for sure on 31 October and delivering Brexit is worth the economic promise fall-out it might cause

And what might a no-deal Brexit look like? Under WTO rules the EU could impose tariffs of 40% on British exports of lamb and beef. The car industry has warned it would be hit by costs of more than £70m a day due to delays at the border in the event of a no-deal Brexit.

There is a serious debate to be had about the 31 October deadline and whether or not the political imperative to deliver Brexit on this day - having delayed twice - outweighs the economic risk of doing so.

:: Listen to the Sophy Ridge on Sunday podcast on Apple podcasts, Google podcasts, Spotify, Spreaker

There will be many Brexiteers in the Conservative party, and around the country, who will argue passionately that there is. A vote was cast three years ago and the social and political discontent grows by every passing day that vote isn't honoured by our politician classes.

We desperately need an honest debate on whether the trade-off of coming out for sure on 31 October and delivering Brexit is worth the economic promise fall-out it might cause: Mr Johnson should make that case.

But to pretend that the UK can leave the EU on 31 October with no deal and tariff-free trade is simply not true. Mr Johnson should show Conservative party members and the public more respect and be straight with the facts.

Sky Views is a series of comment pieces by Sky News editors and correspondents, published every morning.

Previously on Sky Views: Hannah Thomas-Peter - Trump has shifted the boundaries of what is acceptable in public life