Just 37 per cent of English people say they regard themselves as British when travelling abroad; almost half of English voters believe the Union will be split asunder 25 years from now.

Our poll findings reflect the way the devolution settlement has subtly transformed the nation's self-image. The Holyrood Parliament was supposed to assuage the Scottish appetite for independence. Instead it appears to have whetted it.

While there remains, for the moment, a clear majority against independence, the SNP is in power and its skilful leader Alex Salmond will strain every sinew to tilt popular sentiment towards his dream of separation.

Meanwhile in England, there are the stirrings of a new nationalism fuelled by a sense of unfairness. The English feel short-changed, both in terms of a democratic deficit at Westminster and the apparently favourable treatment enjoyed by the Scots, such as state-funded personal care for the elderly and the promise of free prescriptions for all.

This is imposing new and dangerous strains on a Union that is already taken far too much for granted. This year's 300th anniversary went virtually unremarked.

Has any country been more careless of its past? Yet there is so much to celebrate. It is a truism that we have been stronger together than we could ever have been apart.

But Britishness runs deeper than a check-list of historic achievements, no matter how notable. It is rooted in our shared institutions and values - the sovereignty of Parliament, the primacy of the law, the independence of the judiciary, the proud traditions of our regiments, the freedom and vigour of our media.

And, perhaps most important, it is about a state of mind. The British share a temper and outlook that is distinctive and which many across the world find admirable, even enviable. It is a lot to throw away.

In his interview with The Daily Telegraph today, David Cameron rightly eschews the idea of playing to the gallery of English nationalism and stresses instead his commitment to the Union. While genuine grievances have arisen and must be addressed, he warns that nothing must be done that might "threaten it or undermine it".

Our campaign takes that as its starting point as it seeks to foster a debate on how this extraordinary institution can be nourished and strengthened. At its heart is pride in our country, which might seem an old-fashioned virtue - though not, we feel, to our readers who will readily see the true value of being able to Call Yourself British.