SIR JOHN Major and Tony Blair took a calculated risk this week. The two former Prime Ministers came together to warn that a vote to leave the European Union could break up the United Kingdom. What was surprising, however, was where they chose to deliver that message – a city where many people have traditionally been quite keen to break up the UK, or, at least, break off one part of it. Not Scotland, but Northern Ireland.

The two men delivered their warning at a campus of the University of Ulster, not in Jordanstown, on the outskirts of Belfast, or the mainly Unionist Coleraine, but in nationalist Londonderry.

The location was chosen in part because of symbolism.

Where the two men stood was just a few miles away from the border with the Republic of Ireland.

The second main plank of their argument was that a Leave vote would fundamentally change how the border operates, with a huge knock-on effect on the still fragile Northern Irish economy.

But the headline appeal was mainly to the Unionist community.

Tactically, this makes sense. There are more Unionists than Nationalists in Northern Ireland.

Unionists are also more likely to vote Leave, not least because the largest party, the Democratic Unionist Party (DUP), backs a Brexit.

The ex-Prime Ministers are also gambling on the fact that polls suggest Nationalists are less keen on a united Ireland than they were a few years ago, before Ireland's high-profile economic bail out. But at times it seemed a curious message for two former party leaders who had devoted so much of their time to helping the peace process (the impact of Sir John's now little-mentioned Downing Street declaration cannot be underestimated).

And many, not just of her own supporters, will have felt a sympathy with the DUP First Minister Arlene Foster when she accused them of using Northern Ireland to scaremonger and try to frighten other parts of the UK.

That we have moved to a point where, for once, Northern Irish politicians are accusing others of scaremongering is only a progress of sorts. There is an Irish warning that has been mainly overlooked by all sides in this debate.

In 2001 the country surprised the world by voting No to an EU agreement, the Nice treaty. At the time it was seen by many outside as a vote against European expansionism. But part of the live debate in Ireland at the time were proposals to change the rules for smaller countries – and concern that Ireland, with a population of less than four million – could suffer further down the line.

Underlying that was a fear of and a backlash against elites, by many who felt that, despite the then rampant Celtic Tiger, they had been left behind both economically and socially for years.

Stop me when this sounds familiar.

There are few crumbs of comfort for David Cameron in the Ireland experience. As all those who lived there at the time, and I was one of them, will remember, the then Irish Government did not see the No vote coming.