It ought not even need to be said but it did '“ the Tories had to rule out joint authority

In fact, inclusion of this point is of huge significance and of great comfort to unionists.

The government had already issued assurances, via its ministers speaking in Westminster, that it would not introduce joint authority with the Republic of Ireland.

But the need to state such a commitment with force is growing with time, rather than receding.

Dublin is making unhelpful interventions over Northern Ireland – from ministers demanding a Pat Finucane inquiry (something that could only be justified if there were public inquiries into scores of unsolved IRA murders) to demanding that Britain open its Dublin and Monaghan bomb files.

Pronouncements from Irish politicians at times over Brexit sound like statements as to what will, and will not, be acceptable to Dublin with regard to border arrangements.

Meanwhile, the Irish presence at the talks almost suggests equal London-Dublin responsibility for NI.

Ruling out joint authority is also needed given that Tony Blair’s government disgracefully used it as a threat in the 2006 St Andrew’s talks (no significant or comparable threat was ever issued against the political wing of the IRA).

So savour this sentence: “We will not countenance any constitutional arrangements – such as joint authority over Northern Ireland between the United Kingdom and Ireland – that are in any way incompatible with the consent principle.”

The language is pointed, as it must be.

Now the spotlight shifts to unionists, who can make clear to voters that a healthy unionist mandate in this election will not lead to major concessions to Sinn Fein so Stormont can be resumed. The implication of yesterday’s commitment is that direct rule will happen if republicans make a deal impossible.

That assurance would be wasted if destabilising Sinn Fein conduct was rewarded before it even got to that stage.