In out, in out, shake it all about

Labour's shadow Northern Ireland Secretary, Mr Smith, has had quite a lot of stick for his comments about finding a "unique and imaginative" solution to the problem of reinstating a border between Ulster and Eire.

To some extent the criticism was well-deserved, as his suggested solution (Ulster remaining in the EU) is not one that is guaranteed to be achievable, and doesn't allow for 'soft failure'. However, at least he is thinking and talking about it, at least he is putting up ideas.

Even if we fail to agree a deal with the EU, and then the US blocks us from defaulting to WTO rules, we will make do. We survived the 70s and came back. We can survive worse. But failing to settle the border question satisfactorily could well mean the return of terrorism to Northern Ireland, soldiers on British streets, children shot or blown up.

Ulster didn't even vote to Leave - Remain won by a good margin. The EU has been a very good deal for Ulster. They are being dragged out into the cold against their will.

So whatever damage we do to the UK as a whole by leaving the EU, we have a moral duty to ensure that Ulster is not riven again by sectarian violence.

In system engineering fail-soft means that if something goes wrong then the system can still function, albeit below par. Given the chaos at the heart of our government we should be aiming for the best but assuming the worst.

In the worst case scenario (from the point of view of 'controlling our borders' Brexit) there is no border control: EU citizens can use Ulster to enter the UK, while smugglers can effortlessly avoid duty. The smuggling would be more of a concern to the EU than to us so they would presumably institute targeted checks - e.g. on large freight vehicles.

The next step up would be a 'hard but permeable' border. Checkpoints set up on major routes, checking passports but nothing else. Of course, these would be easy to evade if you know the area. This would be easy to build up from the current situation, but wouldn't be much more effective than the previous option.

From there? Well first we need to decide what we really mean when we talk about 'control over our borders', and how much we are prepared to sacrifice to gain that control. A Trumpian solution might even prove popular, given how much support it has there - though I hope that is never seriously considered here.