The smile of the Maitre d' is painfully stitched on as he ushers us to the table. It's not just that we have a small girl with us, though that clearly doesn't help. His face displays a range of emotions, chiefly apprehension and outrage. I don't blame him. This is just how I felt the first time I saw Dave.

"Why does Kevin think I want to know a gang-leader?" I wondered on being introduced by a friend. The Dennis the Menace striped sweater, the skull rings, the leather jacket: these weren't so remarkable. What was extraordinary was the air of throat-slashing menace exuded by this large, saturnine person. The eyes were dark, swivelling orbs that seemed to say: "I'm MAD I am. Ahahahaha!"

Bounding into the restaurant with his wife and small daughter, Dave, even in the unfamiliar guise of paterfamilias, could still provide the Tories with a fine pair of Satanic eyes. He is now a teacher, jauntily spouting tales of pupils bringing guns to school and swapping forged banknotes. Fortunately his stock is currently high with the kids, ever since he (accidentally) bought a pair of the correct expensive trainers: "Their little fists came out - 'respect to Sir!'"

This is the only time the fists come out in class, and I can believe it, having once seen him quell the regulars of a tough Yorkshire pub without even knowing he was doing it. With my back to the wall, I saw the effect of Dave in full flow on a room full of thick-set Tykes. One by one they registered that piercing voice with its hint of plumminess, set their pints down and swivelled heavily round on their bar-stools. Then they clocked Dave, still booming implacably on, and their faces suddenly took on a faraway expression while their fists unclasped and blindly groped for their pints again. He almost cleared a bar in Hampstead once. That was during his stint as graverobber by appointment to the British Museum: one of a squad of archaeologists clearing the vaults of a London church. In the small saloon, he spoke with manic enthusiasm about cutting off the heads of corpses, of coffin-liquor, stench and decay. Only once did he recall faltering, at the sight of a grotesquely ruined face, intact after two centuries: "I didn't like that," he said with the air of someone sending back a disappointing entree. All around us, drinkers were choking and retreating as he rose to a fortissimo climax: "When I get my crowbar under the lid of a coffin and take a good look inside ... I think, life doesn't get much better than this!"

His sturdy daughter, The Gipper, has inherited his stoicism. The high- chair provided by the Maitre d' is much too small and she gets stuck. As her parents wrestle to release her she lets out a fearful shriek, then - and I have never seen any infant do this before - bites it back and sets her lips firmly until she can be extricated. Her small, resolute face reminds me of the day when we found Dave sprawled on the steps of the house we all shared. His girlfriend (now his wife) explained that he'd hurt himself playing football, had walked back but now needed to be helped up to the flat. We hoisted him up like a battering ram; he was heavy and we bashed him trying to get him round the bend in the stairs. He moaned softly, and I remember his white and strangely glossy face shimmering in the gloom.

The next day he hobbled down to the bone clinic at the hospital and hobbled all the way back again because they were too busy to see him. Several days after his fall he was finally taken away in an ambulance, babbling and agonised, having by now walked miles on a leg broken in several places.

When we visited him in hospital, he had been moved off the main ward to protect the sanity of the other patients, as he never stopped talking. We found him tucked in a private room, ostentatiously reading a copy of Men Only which had Woman's Own tucked inside it.

It is gone midnight and we have an early start in the morning, but Dave is still talking animatedly and waving his arms about, and I suddenly realise that I have never, in all the years I've known him, seen him snooze, yawn or even look tired. He tells us about being thrown out of a shared student house after he sleepwalked into a girl's bedroom, stark naked. In tones of boundless menace, he had hissed at the cowering girl: "Don't worry, it's only me." I'm glad there were two locked doors between us when I slept under the same roof as Dave.