For such a prolific chronicler of other writers' lives, Peter Ackroyd can be exasperatingly reticent about his own, as Donald Clarke finds out

What I have read of the home life of Peter Ackroyd, novelist, biographer and obsessive chronicler of London, leads me to believe that he prefers to avoid the company of others. When I say as much he screws his broad, fleshy face up into a tight purse, looks accusingly at me and answers with italicised firmness: "As much as humanly possible." Well, I'll get my coat then.

Ackroyd has made his way (I want to say grudgingly) to the Basil Street Hotel in Knightsbridge to discuss his new novel, The Lambs of London. Like virtually every one of his published works the book concerns itself with the texture of the most unshapely and unknowable of the world's great cities.

Set in the very late 18th century it imagines a connection between the essayist and critic, Charles Lamb, and the notorious William Ireland, who, among other outrages, forged the "lost" Shakespearean tragedy, Vortigern.

Bustling into the hotel bar, Ackroyd, a burly man with a heavily moustached, slicked-back look more common among bookies than biographers, apologises for being late - he was, somehow inevitably, "reading a book on the Thames" - and settles in to explain what attracted him to Ireland's story. The trouble is he can't seem to remember much about it now.

Are the quotes from Vortigern accurate?

"That I can't recall," he says. "I think I may have made some of the quotes up."

Is the text of the play still in existence?

"I think it does exist, but I don't think I have read it," he says. "Yes, I think it exists in the British Library. I never bothered to read it because I reckon I could make it up as well as Ireland could. But I bet you can't distinguish the real fake from the fake fake in the book."

Well, from what he says neither can he. Unless Ackroyd is having me on (and I think he might be), he appears to be less familiar with the content of his own books than I am. I mention an incident in his exhilarating 1995 biography of William Blake.

"Oh, I don't really believe that happened," he admits. But he said it did. "Do I? Oh, I suggest that, do I? Well, I don't believe it now."

I throw a quote at him: "Infinite London can only be seen within mundane London."

"Who said that?" He did. In London: The Biography.

"I suppose I was talking about the efforts of writers like Dickens and Blake to create a symbolic universe out of their experience of the city," he says. "Presumably that is what I was getting at."

It is curious to come across a writer who does not appear to be any sort of authority on his own work. He is, however, even less useful on the details of his private life. As we move into this area, he curls up in his seat, sighs melodramatically and focuses on an apparently fascinating square of wallpaper over my left shoulder.

Why is he so protective of the inner Ackroyd?

"I just don't think it is of any interest to anybody," he says. "There isn't much of it, for a start."

But he must appreciate the irony here. As a biographer of Blake, T.S. Eliot and Dickens, he is professionally concerned with the private lives of writers. He can't deny that such details colour one's understanding of the work.

"But I never discuss the private lives of my subjects," he says. "Well, I try not to pry at least. I suppose it is rather ironical, but nonetheless true."

Ackroyd was born in 1949 and raised in a housing estate in the unfashionable west London suburb of east Acton. His father, an artist, vanished when he was young and he grew up under the protective gaze of his mother, who worked in an engineering company. With no great encouragement from any mentor, the young Ackroyd fell into reading. Boys who live their early lives as only children to single mothers (as this writer can attest from personal experience) often gain a particular appreciation of the joys of solitude.

"Yes, that may well be true," he says. "I wouldn't know, of course, but I assume it might be true. I assume also that children who are interested in books prefer solitariness. But that may be cause and effect; it may actually be the other way round. Reading is just something I picked up. There are some people who seem to be doomed to be lost in books from an early age, just as some kids seem to be doomed to be railway-spotters or cinema- frequenters."

Ackroyd proved to be a smart kid. He won a scholarship to the local Catholic school and then, in 1968, another to Clare College, Cambridge, eventually graduating with a double first. It takes quite a leap of imagination to imagine the slightly fogeyish Peter Ackroyd, who in Notes for a New Culture (1976) claimed that English culture had, since before the second World War, been on its way to hell in the proverbial hand-basket, as a student during those hairy, dissolute times. As is often the case when questions are put to him that he doesn't like, he seems (or pretends) to misunderstand the line of argument. Did he ever own a rock-'n'-roll record?

"What you mean?" he says. "Like 1950s music? No. We didn't listen to that music."

No. I mean a record by Jimi Hendrix or Janis Joplin or Bob Dylan. Did he indulge in any of the debauchery for which the era was renowned?

"It's difficult to retrieve one's steps from so long ago," he says. "I wasn't a young fogey, if that is what you mean. We used to listen to all the latest records like, erm, James Taylor. It wasn't as if we lived in some hermetically sealed world and listened to Purcell."

I certainly can't imagine that Ackroyd, who has never made any secret of his homosexuality, was ever part of the gay social scene that was beginning to emerge over-ground at that time.

"Oh God no. I would rather shoot myself," he says.

After studying at Yale, he returned to England intending to be a poet, but he quickly deduced that "like English drama in the 19th century", poetry was in terminal decline as a literary form. His first novel, The Great Fire of London, was published in 1982 and was followed in 1983 by The Last Testament of Oscar Wilde and then, triumphantly, by 1985's ingenious Hawksmoor.

It was already apparent that Ackroyd's work was forming itself into a wildly cluttered, densely peopled chronicle of the city of his birth. Like such writers as Iain Sinclair (whose long poem, Lud Heat, was an inspiration for Hawksmoor) and the brilliantly eccentric Michael Moorcock, Ackroyd has found the variety, age and confusion of London a constant source of inspiration.

His most comprehensive attempt to make sense of the city came with 2000's London: The Biography. The fact that he called it a biography suggests that he believes the city to have something like an individual personality.

"Yes I believe it has acquired a personality," he says. "Because of the intimate connection it has had with human beings it has evolved into a human thing. Rather like the Thames has always been considered to be a he or a she, so too the city can be depicted in that way. It is obviously male by default - noisy, loud - rather like your typical Londoner. Whether the Londoner or the city came first, I don't know."

He claims that he was not the sort of boy who collected brass rubbings from Hawksmoor's churches or learned street traders calls for sport. Indeed, as he tells it, it was researching the books that inspired his interest in the city rather than the other way around.

"It wasn't something that I had explored or experienced in advance," he says. "It all began when I began writing Hawksmoor."

However the enthusiasm began, it has, over the years, fuelled something of a one-man industry. Earlier this year he presented a TV series based on the London biography and published a short life of Chaucer (son of a London vintner). Next month, The Lambs of London will be published, then later his book on the Thames and, somewhere in between the two, a biography of Shakespeare (a west midlander admittedly, but no stranger to the capital). Where on earth does he find the time? A grumpy shrug.

"I'm surprised I don't have time to do more," he says. "Well, actually I do have the time. I mean I'm surprised I don't do it."

Yet he had a heart attack a few years ago. That sort of thing is supposed to slow a man down, to make him re- evaluate, but this idea makes Ackroyd cast his eyes to heaven with such vehemence that I fear he may detach a retina.

"Oh, that made no fucking difference," he says crossly. "I was on my feet in two or three days."

So he indulged in no re-evaluations at all? "No! The only thing I worried about was where I was going to get my shirts laundered," he says. "Dwelling on the minutiae of one's own personal mortality always struck me as otiose and silly."

Well, if he doesn't mind me asking, what about the death of others? Ackroyd's partner of 20 years, Brian Kuhn, to whom Blake is dedicated, died of AIDS in 1994. That sort of trauma must surely change a man.

Another puff. More eye-rolling.

"No. Why should it?" he says.

Gosh, he is exasperating. Because such things do change people. If nothing else, it must have brought home - oh no, I am suddenly aware that I am about to be otiose about the minutiae of his personal mortality, the, er, um, unavoidable inevitability of his own death.

"Well. The death of a fly could do that!" he says. As he is now already annoyed, no harm can come of asking him about one of the great legends that surrounds him. He clearly has been waiting for this and, with a mournful groan, he finishes my question for me.

"Oh, the drinking!"

Well, yes. It has been rumoured that he can really put it away. Indeed, a profile in the Guardian last year suggested (rather unfairly) that he is famous for two things: London and drinking.

"What am I doing right now?" he asks.

Drinking Perrier.

"l thank you. Actually, I haven't drunk anything for three weeks and I don't intend to for months," he says. "How could I have written all these big books if I was drinking all the time? It would hardly be possible. It is not lies, but I was never a boozer in that masculine sense, in the sense of [sucking-tart-lemon face] public bars and, if you don't mind me saying so, Dublin."

It must be all he can bear to sit here with me.Suddenly - and delightfully - he breaks into a great big, hearty guffaw.

And, when the tape recorder is turned off, we talk pleasantly about Iain Sinclair, Peter Hall, London traffic and John Banville. But he clearly wants to be gone. Eventually, after a brisk handshake, he stands, swivels and sighs of relief propel him out into the teeming masses of the Brompton Road.

The Lambs of London is published by Chatto & Windus on August 5th, priced £15.99