Owen Polley: Unionists should not rest until every potential Alliance voter sees magnitude of party's plan to weaken NI's place in UK

His intervention appalled unionists and delighted nationalists, who - in connivance with the Alliance Party - have been using Brexit to try to loosen Northern Ireland’s ties with Great Britain and edge it closer to the Republic of Ireland.

Mr Clarke has made many constructive arguments over the years, from the moderate wing of the Conservatives, but his comments about Northern Ireland have been pitifully few and often betrayed a patronising disdain for this part of the UK.

After his former party leader, David Cameron, formed an electoral pact with Ulster Unionists, Clarke told the Daily Telegraph, “you can always do a deal with an Ulsterman, but it’s not the way to run a modern, sophisticated society”.

Nationalists will applaud anyone who supports their schemes to dilute Northern Ireland’s position in the UK.

It is Alliance’s demands that we stay in the Customs Union, irrespective of what happens in Great Britain, which are much more insidious and demand the strongest response from unionists.

The party’s stance of the constitutional issue has recently become one of awkward neutrality. Yet it’s thinking has become so disordered by Brexit that it’s prepared to undermine the principle of consent, risk the Northern Ireland economy and flirt with separatism, in order to resist the inevitable.

Alliance draws its support overwhelmingly from the east of the province, where economic and social links to the rest of the UK are strongest.

Traditionally its supporters are in favour of the Union, but they’re often comfortably off, middle-class people, who view some of the more confrontational aspects of local politics with distaste and prefer to avoid the label ‘unionist’.

If they don’t work in the public sector, they’re likely to own or be employed by companies that do the vast majority of their business with the rest of the UK.

They probably work and socialise with friends or family from the rest of the country and they may have children who live in Great Britain or attend universities there. In other words, these are some of the voters who would be affected most by internal UK border controls.

Do they realise that their representatives are prepared to make it more difficult for them to work and travel within their own country, in order to prioritise connections with the Republic of Ireland?

If that hasn’t yet been explained to them properly, or the deadening effects it could have on their prosperity, then unionist parties should not rest until every potential Alliance voter is aware of the magnitude of what that party is proposing.

The prospect of any arrangement or ‘special status’ that keeps Northern Ireland in the Customs Union while the rest of the UK leaves is a serious threat to the Union that shouldn’t be underestimated.

Nationalists are pushing the idea precisely because it would bind us more closely to the Republic and weaken our links with the rest of the UK significantly.

The current government is vanishingly unlikely to accept a border at the Irish Sea while it relies on DUP votes and faces an ongoing separatist challenge in Scotland.

However, the Conservative administration is weak and, if Jeremy Corbyn were prime minister, he’d certainly be more receptive to nationalist demands, particular if they’re given a cross-community veneer by Alliance’s collusion. Things can change quickly in such a volatile political climate.

That’s why unionists must make absolutely sure this type of ‘special status’ gains no momentum.

If an internal border with the rest of the UK were imposed on Northern Ireland, it would represent a betrayal to make the Anglo-Irish Agreement look trivial in comparison.