The momentum is now unstoppable as the previously unionist Mail on Sunday demands...THE BREAK-UP OF THE UNITED KINGDOM

You've probably already seen this, but it has to be one of the all-time classic newspaper front pages.  Today's Scottish edition of the Mail on Sunday declares that Scotland is an "OPEN DOOR FOR TERROR" on the grounds that the paper's "investigators" (I rarely say LOL, but LOL) were able to take a ferry trip from Belfast to Cairnryan without encountering any "border controls" or having to show their passports.

There is of course a remarkably simple explanation for this shocking lack of border security.  The "investigators" didn't actually cross over an international border.  As most people have discovered by the time they leave primary school (let alone by the time they have editorial control over a national newspaper), Northern Ireland and Scotland are both part of the United Kingdom.  A ferry crossing from Belfast to Cairnryan is therefore a routine domestic voyage.  Having to show your passport on such a trip would be quite literally as daft as having to show your passport on a ferry between Mull and Oban, or between the Isle of Wight and Southampton.

I'm just about old enough to have done that trip (or rather the very similar Larne to Stranraer crossing) on three separate occasions during the Northern Ireland Troubles - in 1990, 1992 and 1994.  Even back then, there were no passport checks, and in fact there wasn't much in the way of ordinary security - a far cry from the heavily militarised international border between Northern Ireland and the Republic of Ireland.

The amusing part of all this is that there is only really one way to introduce the kind of hard border between Scotland and Northern Ireland that the Mail on Sunday are demanding.  And that is for Scotland and Northern Ireland to cease to be part of the same state.  Scotland will have to become independent, or Northern Ireland will have to leave the UK.  Either way this is a long distance from the Mail on Sunday's previously rock solid British nationalism, and is a development to be greatly welcomed.