ALL around me identities seem to be crystallising, hard as diamond. Not mine. People seem so sure of who they are, so unwavering. Not me. For me, identity is fish-slippery, constantly changing, always untrustworthy.

Everyone else seems to know – or at least pretend to know – precisely where they come from, who they belong to, and what that means for them and their place in the world. They’re either a 100% true Scot, or British born and bred, or as English as Orwell’s old maids biking to Holy Communion through autumn mists. Welsh as the valleys. A proud Irish patriot.

I’m none of those things – and also all of those things. I’ve been stuck on this weird planet, on this freezing, crazy archipelago, for 50-odd years, and I still don’t know what or who I am. I live in awe, and a little fear, of people who’ve the certainty I lack. I don’t understand their "passionate intensity", as Yeats put it. Yet every month now some new study emerges telling us that whether its English, Scots, Irish or Welsh, people’s sense of national identity is becoming ever more fixed and concrete.

Identity has always tormented the hell out of me – probably because I’m an absolute mongrel of a creature. My family is Irish, Scottish, English, Welsh – with some Russian, German and Jewish thrown in generations back. I was born in London, raised in Northern Ireland and live in Scotland. One quarter of my immediate family is Cockney English, another quarter loyal British Ulster. The other half, though, is Irish through and through. One grandmother was an intelligence officer for the "old" IRA during the 1919-21 War of Independence. The other in the British army during the Second World War. I’ve men on one side who picked up a gun for the Irish Republic, and men on the other side who picked up a gun to keep Ulster British.

I could never navigate the maze these competing bloodlines demanded. I began to realise something was off when I was about four and shopping with my mother in Belfast one weekend. There were bombs and running and blood. I don’t remember which particular atrocity this was, but it’s the atrocity that set in place the first stumbling block of identity; it tripped me and I’ve never really regained my balance.

Like any child, I was traumatised at this first experience of war, for that’s what "the Troubles" – a deeply misleading euphemism – were: war. I think I asked: ‘Which side are we on?’ By the time my parents finished talking, I realised I could be on neither side. My parents’ marriage was "mixed" – a phrase which itself explains the profound dysfunction of identity in Northern Ireland: one Catholic and one Protestant. I wasn’t christened; I was raised without religion, for which, ironically, I thank any God that may exist.

So if this war going on around me was based on both religion and ethnicity – British v Irish, Catholic v Protestant – how could I, who’d a Catholic and Protestant parent, and English family as beloved as my Irish family, take any side? To pick, would be to wish ill – even death – on the other. Choosing an identity would become a form of psychological suicide, and intolerable rejection. Little wonder, then, that the punk song Identity – "Identity is the crisis can’t you see" – by X-Ray Spex seemed to speak directly to me as a kid.

The one part of my identity that didn’t wobble like jelly was class. I’d grown up poor. But eventually even my working class sense of self got jumbled. I’d the ability to pass exams with relative ease. I passed enough exams to get into one of Northern Ireland’s best schools – yet that made me suddenly different to all my friends and neighbours. I played rugby and studied Latin. My teachers told me I could be anything I wanted. Back in my housing estate, my friends were warehoused at school and told to apply for dead-end jobs. Then I was off to two of Britain’s best universities. I was still working class – I still am working class, you can never not be working class if you know what it’s like to go to bed hungry as a kid – but I was no longer "of" the working class, no longer living among my working-class friends and family, but with the middle-class people I found myself surrounded, and often bored, by. The middle class can be tedious.

The other part of my identity that was once wobble-free was my atheism. Growing up in that "mixed" family amid sectarian hatred taught me to despise organised religion. After I left Northern Ireland – to raise a young family away from violence, here in Scotland – I started to discover that folk who believed in God weren’t all bad. Today I’m a conflicted atheist with deep respect for believers, as long as they walk the walk and don’t just talk the talk.

Looking back on 30 years in the media, I now realise I spent nearly all my career exploring identity, attempting to understand the terrible certainty others had that I didn’t possess. First as a young reporter, trying to make sense of why people in Northern Ireland murdered their neighbours over a flag; then as a writer unravelling neo-nazism and Islamist terror and how identity can drive extremism. I recently received an email from someone who’d read two of my novels. They asked why the theme of identity ran so strongly through both. That made me shiver. I hadn’t thought either book explored that dangerous, bitter multi-headed monster.

Today, I’m rather excited about the prospect of grandadhood. Both my children are adults. And I think that’s where my true identity lies, in being a dad, a husband and one day soon, I hope – are you listening, children? – a grandfather. For years, I thought I was cursed by my lack of fixed identity, of never feeling like I belong. In fact, I now reckon I was lucky, even blessed. To love my family is identity enough. My life may have been very different if I’d loved a country or a flag.

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