WE were talking identities across an Edinburgh dinner table the other week. I was explaining that, by origin, I am only half a Scot.

The other half is Irish. My mother hails from farming stock, from that lush crescent of countryside

around the North-western corner of Loch Neagh.

She left the family smallholding to join her older sister on Clydeside at the age of 14 and, apart

from fondly-remembered family holidays in a white-washed cottage, picking wild strawberries up country lanes and helping bring in the hay harvest, she has seldom returned. My own most recent attempt to revisit that part of my roots, to speak at a conference in Belfast, left me fog-bound - and speechless - for five hours at Glasgow Airport.

''Where exactly was the farm?'' another guest across the table inquired. ''The nearest town is Magherafelt,'' said I. ''Why,'' she exclaimed, in a neatly-modulated home counties accent, ''that's where I live.'' The coincidence instantly reminded me of another Edinburgh encounter, this time in a Rose Street public house some 20 years back, when a friend of a friend persisted in quizzing me about my origins.

''I was born and grew up in Greenock,'' I insisted, as he - claiming a professional expertise in the finer subtleties of accent - probed deeper into my antecendents. ''Any family connections with the Ballymena area?'' he finally ventured, in a gambit which hit bull's eye and left me literally speechless. Ballymena lies just a few miles to the north and east of Magherafelt. I

had thought my Irish roots were hidden deep in my genes and my Scottish upbringing. Here was proof that, to the keenly-tuned ear, other more accessible traces of a split identity survived.

Identity will play an increasingly central role in the politics of these islands over the next few years. It already dominates debate in that fractious part of the island of Ireland where my mother was born and where, today, Mo Mowlam doggedly pursues reconciliation against daunting odds.

It is bound to play a significant part in the run-up to next year's elections to the Scottish Parliament and later, as the new legislature feels its way around the twin roles that will inevitably be thrust upon it - physical manifestation of the precise powers devolved to it by statute but physical manifestation, too, of Scottish popular will.

And, as 11 out of 15 member states of the European Union prepare to share one of great symbolic signifiers of national identity - their currency - we can expect fresh momentum to be breathed into that contentious debate, too.

''In a devolved Britain,'' writes Michael Ignatieff in the latest issue of the magazine Prospect, ''civic and ethnic identity will surely be ever more completely sundered. For the nations of Britain may share the same history, but they do not believe the same myths.'' Ignatieff goes on to argue that the silences on which British identity once depended have been comprehensively broken.

''Once broken, they reveal the extent to which we live in a plural moral world. In belief systems, we are no longer of one faith; in our private lives, we are no longer within one family model; in the nation itself, no longer under the stable or uncontested domination of the English; and we no longer belong to a community of common origins. We are living in what Isaiah Berlin called a ''pluralist world of incommensurable and sometimes incompatible visions of the good''.

You can see these ''incompatible visions of the good'' in the festering internal wrangles between New and what the party modernisers like to characterise as Old Labour. Not even the most artful doctor of spin could credibly characterise John McAllion or Bob Thomson as other than honourable and long-serving foot soldiers of the Labour movement whose deep-rooted sense of political purpose simply happens to be out of joint, on a number of key fronts, with the prevailing Blairite orthodoxy.

You could see that same incompatibility, this week, in the dissenting grumbles of French socialist deputies, as Tony Blair tore up the left/right political template in their own language and beckoned the Jospin government down his ''troisieme voie''. But you can see it too in Blair's own reluctance to join the first wave rush to monetary union and in his warnings to Brussels to stop interfering too deeply in taxation and welfare issues in member states or risk a popular rebellion against loss of national identity.

And back in Britain, those same incompatible visions of the good surely lie behind the national sport of Dome-bashing and the relentless teasing of Peter Mandelson. I'm sure the Minister without Portfolio believes sincerely in his mission to build an experience at Greenwich that will knock all our socks off, just as he is incorrigibly committed to his larger-scale project to rebrand these islands as Cool Britannia, the epitome of millennial style and grace.

But the half-stifled guffaws that now routinely seem to greet any mention of his name indicate that large numbers of people on these islands simply refuse to share the Mandelsonian vision of what is good for us. They are responding to the Dome's inevitability and the realisation that Mandelson's not for turning with the only weapon left to them. Withering wit and humour.

If we no longer believe in the same things and no longer originate from the same place, argues Ignatieff, we more than ever need a network of civic institutions we can all trust. But if what he calls a strong ''civic core'' is the only basis left for forging a common identity, there is another huge problem looming.

At no point in my life has it been harder to define what we mean by a civic core. In this age of private finance initiatives, when commercial imperatives are being introduced to the very heart of the civic realm, it gets harder and harder to see what - other than the disciplines of the market place - binds us together in a common sense of purpose or a shared vision of the good.