Avoiding the return of hard border in Ireland is likely to prove “unsustainable” in the event of a no-deal Brexit, according to the leaked documents.

Boris Johnson has insisted that technological solutions and a “can-do spirit” will prevent a hard Irish border.

But the contingency planning for no-deal prepared by his own government suggests that a hard border is all but inevitable, leading to “direct action” and road blockades.

The document reveals that there will be “no new checks, with limited exceptions” on the border between Northern Ireland and the republic.

But significantly it goes on to say that although measures will be introduced to “avoid an immediate risk of a return to a hard border on the UK side”, this is “likely to