The worst whisky I have ever tasted is still on the market, although it has disappeared from my-local Co-op, where I once bought 15 bottles as Christmas presents for contributors to a newspaper diary I was then editing.

I shall call it Murdock, for that is its name, and it tastes like the mixture of paraffin and petrol some elderly tractors run on. Not that I am in the habit of drinking petrol and paraffin. It's just that siphoning some off to light a fire once led to some unexpected imbibing. It was, I must say, a lot better than Pernod.

Among those who received a bottle of Murdock was a journalist with strong connections to one of the top Scotch whisky conglomerates. He was so disgusted he immediately arranged for the diary to be sponsored by the firm in question, with bottles of a top 15-year-old malt made available for tip-off fees. As he would have received approximately two a week, perhaps his initiative was not entirely selfless.

The word whisky comes from the Gaelic uisge beatha, or water of life, a term echoed all over the world in distilled spirits from schnapps to pisco: Pint of aquavita, pal, soon as you like. Neil Gunn, in his seminal and, I always think, somewhat inebriated work, Whisky and Scotland, argues not only that whisky is a source of revolutionary nationalistic fervour, but a kind of selective anaesthetic which has rendered the worst indignities of Scottish life - gross industrial poverty, exploitation by a southern neighbour - easier to bear.

The fine line between this and the complete dulling of hope, the defusing of the intellectual impulse to change, has been crossed too many times by the so-called roaring boys of Scottish culture and politics. As the Scottish labour movement has moved from an almost complete identification with temperance through macho bevvying to an ill-worn pseudo-moderation, casualties litter the halls of Westminster as they will the closes of the Mound and the cobbles by Holyrood.

We seek brilliance and oblivion in whisky, sometimes both at the same time. But the destructive nature of the water of life will, in the end, always win.

This came home to me very forcibly at a recent Edinburgh Book Festival session on alcohol and cultural identity, at which I found myself sharing a platform with Vitali Vitaliev and the poet Simon Armitage. A woman in the front row began her question by telling us about her alcoholism, and suddenly all the theories of national-nature-through-type-of-beverage and my own tasteless jokes about gender politics (the only person who ever drank me under the table was a woman . . . but then, she did come from Inverness) crumbled away like rotting bar-room floorboards. I felt myself falling, head spinning, uncertain, struck dumb.

We stumbled on, talking, as Vitali pointed out, fuelled only by entirely inappropriate glasses of water. And I thought of my wife, whose job involves almost daily medical intervention in the twisted, sad, desperate lives of alcoholics, and her reaction to the film Leaving Las Vegas: where, she wanted to know, was the shit on the sheets, the blood on the breakfast table, the beaten wife, the caked vomit on the clothes kept on for a week? Where was the falling asleep in a ditch, the starved and bruised children, the sordid, seamy grime of drink unleashed? The glitter of Nic Cage's Nevada night seemed very far away from Scotland.

I thought of a friend, charming, sophisticated, successful, who can apparently consume huge quantities of fine wine and good beer without ill-effect. Until he touches whisky. Not vodka, not gin, just uisge beatha. And who then almost instantaneously turns into a vicious, belligerent, sexist piece of central Scotland white trash. Afterwards, in his right mind, he grins, and says, hey - it's a Scottish thing. And we forgive him. But we don't forget.

There is a scientific argument that some of the impurities that give whisky its taste and character - congeners - are poisonous and more than capable of causing nasty allergic reactions in some vulnerable souls. And yet the big, dark Islay malts, reeking of peat and seaweed, and packed full of congeners, are much less prone to giving me hangovers than the hateful Murdock, which is, I fear, almost pure industrial grain spirit, aged for the legal minimum of three years.

Maybe it is, truly, a Scottish thing, and the mixture of my genes with some from Ireland and Wales, not to mention being born in England, excludes me from the purity of the water-of-life experience, the crazed descent into what it means to be a true Scot.