Varadkar confirms Dublin's aggressive stance on the border

In this stance it has, it seems, the full support of Michel Barnier, the Brexit chief negotiator, and the other key EU figures Donald Tusk and Jean-Claude Juncker.

The Taoiseach Leo Varadkar is now stating that a deal must be done by October, or Northern Ireland would continue to follow EU regulations.

These tactics from the Republic of Ireland are highly aggressive. It is to be hoped that people of influence within the Conservative Party are making a clear mental note.

But in one unintended respect Mr Varadkar’s latest comment is helpful.

If there is clarity by October then unionists will at least know whether London intends to follow through on its intermittent commitments on the border.

That will be a life or death moment for the coalition, which in any event faces multiple challenges.

This problem is not going to go away, unless Mr Varadkar is suddenly going to find himself isolated by the EU, and there is no indication whatsoever that that is going to happen.

The UK government failed in recent days to rule out Northern Ireland staying in the customs union and single market in all eventualities, even at the very end of the process, regardless of whether or not there is a deal. Such a scenario would immediately make the Province a semi-detached part of the UK, and would be Sinn Fein’s biggest gain since NI was founded.

The British government has been so weakened by last year’s general election that it has not even been prepared to bluff its preparedness to crash out of the EU without a deal.

The UK negotiators ought at least to convey a clear determination to countenance such an outcome.

And the situation is fast arising in which the DUP might have to convey a similar determination to topple this government in the absence of a cast iron guarantee on the border.