At the hacks’ hustings for the Tory leadership candidates, I asked the five who could be bothered to be held to account by your inky fingered servants a really boring question.

Would they accept the definition of a "hard border" on the island of Ireland written into the December joint agreement between the UK and the EU, which underpins the backstop plan in the Withdrawal Agreement?

The reason this matters is that the joint agreement says there is a commitment to avoid "a hard border including any physical infrastructure or related checks and controls", and the Withdrawal Agreement says "any future arrangements [for Ireland] must be compatible with these overarching requirements".

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Sajid Javid says he thinks he has enough backing to progress through the second stage of voting. Credit: PA

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If you are still awake, the reason I asked this seemingly dull technical question is it is this definition of a hard border that sunk Theresa May’s stoic attempts to have her deal ratified by MPs and ultimately sunk her.

To be clear, it was completely understandable she agreed there should be no hard border - because prior to the Good Friday Agreement the previous hard border was associated with terrorism, crime, life-wrecking atrocities.

So of course neither May nor the EU could countenance a return to a hard border.

Rory Stewart and Jeremy Hunt are both running to be the next PM. Credit: PA

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The question is what a hard border actually means. And the framing of "hard" as meaning "any physical infrastructure or related checks and controls" necessarily compelled May to accept that all of the UK would remain in the customs union for as long as it takes to find alternative arrangements to obviate the need for customs checks and that much of Northern Ireland would be subject to EU rules to avoid the need for product and food quality checks.

In other words this framing of "hard" led directly to the refusal of many Tory Brexiters and the DUP to back her deal - because for the DUP it drives a wedge between NI and GB, and for Brexiters it keeps Brussels in charge of much of the UK economy.

Boris Johnson did not appear at Monday's hustings. Credit: PA

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And although the backstop to keep this border open is to be "temporary", how could it ever melt away if physical infrastructure and associated controls are explicitly and permanently prohibited.

If any kind of technological solution is banned - as it appears to be - only the Brexit fairy can get rid of the backstop.

Which is why I asked the five available candidates whether they would try to change the definition of a hard border.

And the answers were:

Gove - no

Hunt - “broadly” no

Stewart - no

Javid - not sure

Raab - probably, but thinks the definition is more ambiguous than I say.

Michael Gove and Dominic Raab are both in the running to be the next Tory leader. Credit: PA

For what it is worth, I assume Johnson - if he had deigned to turn up - would have agreed with Raab.

What flows from all this?

That in substance Gove, Hunt and Stewart would struggle to get Brexit approved by MPs, because the DUP and ERG Brexiters will struggle to understand why the backstop isn’t as toxic as it ever was.

And Johnson and Raab would probably be told by Whitehall if they want to change the hard border definition they can whistle for it - and that what they really want is a no-deal Brexit.

And Javid is yet to make this ultimate Hobson’s Choice.

Oh the toxic legacy bequeathed by May to her successor, party and country.