The other day, on a radio discussion programme, I heard Michael White of the Guardian refer to Tony Blair as a middle-class southerner. Nobody picked him up on it, but I am sure that if they had done he would have stood his ground. He is a true Gu ardianman. No Guardian man can conceive of the existence of a middle-class northerner. If Mr Blair is middle-class, it follows that he must be a southerner.

One often hears it said that Mr Blair, as leader of the Labour Party, will appeal to the southern voter. It would be fresh, strange even, to hear it said that he will appeal to the northern voter. The idea that he will appeal to the southern voter is as yet untested electorally. But Mr Blair has already proved himself on his home ground, in County Durham, and this seems, mysteriously, to count for nothing.

If Mr Blair were a German politician from a similar class background, he might have grown up speaking in two ways: in his local dialect and in Hochdeutsch or Standard German. As a politician in Bonn, he might have spoken Standard German, while at weekends, back home, he might have taken pride in reverting to dialect. He could have been both middle-class and unmistakably, say, Swabian. But this option has never been open to the English - or at least not for centuries.

Mr Blair is not a class traitor. He grew up speaking the way he speaks now, as I clearly recall from the brief period during which our school careers overlapped. At the age of eight he looked and sounded exactly as he does now. Other pupils at Durham Chorister School were sent there precisely in order to purge the dialect from their systems and in one celebrated case a boy's father came to the school to complain that his son was still using bad language. The teacher, Mr Watson, inquired wha t sort of language the father meant. The example given was the word "clag" (meaning to stick something together).

At the next lesson Mr Watson announced that none of our class was to use the word "clag" ever again, on pain of a "fleabite" (one stroke of the cane). And the results were predictable. Clag, which most of us had never heard before, became a vogue word. It was clag this, clag that, clag the other. Mr Watson himself, who nearly lost control of his carpentry lesson, became known simply as Clag.

But Mr Blair was never a clag-merchant. He has not cleansed himself of his northernness, nor done what Harold Wilson did, which was to convert to an Oxford accent as an Oxford don, and then brilliantly revert to northern as the occasion seemed to require. There is nothing inauthentic in Mr Blair's act. It is the common notion of northernness that is inauthentic.

As it happens, I was overlooked as Mr Blair's biographer, but if I hadn't been I would have tried to reconstruct what his days were like. He was a "day bug", third in pecking order after chorister and boarder. He lived, I read somewhere recently, on the other side of the cathedral from the school, that is to say in or near the castle.

Every weekday he would have put on a uniform of short grey worsted trousers, purple-trimmed blazer, purple-topped socks held up with elastic garters and a purple cap. Satchel in hand, he would cross the castle green in the direction of the cathedral. Then came an interesting choice. If he went left, cutting down into North Bailey and passing between St Chad's College and the Chapel of the Nine Altars, which forms the cathedral's eastern facade, he would reach an ancient stone gatehouse, leading into wha t is called the College (the cathedral close), at the end of which he would see the weathered stone archway to the school.

But if he was adventurous, another route lay open to him. He would pass, as the Judges of Assize would pass, directly from the castle to the north door of the cathedral, where he would be impressed by the stern beauty of the Sanctuary Knocker, with whichfugitives of yore would demand asylum from their enemies. Plunging into the august gloom of the mighty Norman building, Blair would have crossed the nave alongside a stone line in the floor which marked, in monastic days, the farthest that women could come into the cathedral.

Perhaps at the centre of the nave he would have turned to the High Altar and bowed, as the choristers did. Perhaps, in sight of the Neville screen, he would have wished himself a chorister and not just a boring old day bug. Perhaps he would vow: still, I'll show them - one day I'll be a rock star, and prime minister of the country.

Proceeding through the south door, Blair would enter the cloisters, passing the steps to the Monks' Dormitory, which held such priceless relics as St Cuthbert's Cross, then a door that was rarely opened, which led to a mysterious muniment room, then a vestry and finally, turning right into what would at first seem like pitch darkness, he would descend into the crypt.

Later converted into a coffee shop, the crypt in those days was a repository for some decrepit statuary and, surprisingly, the skeleton of a whale - a relic of the days when the prince bishops of Durham (whose palatinate purple we have already encountered in Blair's uniform) claimed a right to the beached whales on the Durham coast (a claim which took precedence over even the king's).

So Blair might have stopped there in the Stygian gloom and damp, and the whole weight of the history of Durham might have come crashing down on his shoulders - the Lambton Worm, the Battle of Neville's Cross, the world of the border ballads, the prince bishops, the Sanctuary Knocker ... You see now, perhaps, how much of history is air-brushed out if we insist on Blair as a middle-class southerner. You see how romantic this northern childhood must have been. And I haven't even thrown in a black pudding,

or a slab of Ma Hattersley's parki n.