Faster than many realise, the time is coming to think dispassionately about the unification of Ireland. When the expected border with the rest of the UK is established in the Irish Sea the case for reuniting north and south will get its biggest boost since partition in 1921.

I suggest this may not be a bad thing. Before describing unification on the whole island of Ireland in the language of the “break-up” of the UK we should remember that there will be a corresponding coming-together. We should think about the gains. The idea makes so much sense.

“It is hereby declared” (says what has come to be known as the Good Friday agreement between the British and Irish governments) “that Northern Ireland . . .