He's glum, he's 55 and he sang at Hyde Park. So who listens now?

"Don't write that we're all old hippies," said the Dylan fan, short-haired, hatchet-faced and over 40. He walked off across the bookshop, handing out set lists for yesterday's Hyde Park concert like forbidden pamphlets.

And he was right, up to a point. The other 30 people, crammed into Helter Skelter off the Charing Cross Road, central London, for a wet Friday evening's Dylan discussion, had not a tie-dyed garment between them. But they weren't young: heads tended to greyness, leather jackets avoided offence. Well- worn hands slipped the set lists into pockets like pounds 50 notes.

Chris Whithurst stood by the door wearing a double-breasted jacket over a T-shirt. His hair was long for an executive at London Electricity, and he had already been to the concerts in Liverpool and Utrecht earlier in the week. "I saw Dylan in '66," he said. "There's a lot of people I know from following him around. We meet up socially."

The hatchet-faced man sidled up. He would not give his name, but wanted to say his wife had danced onstage at Utrecht. She bobbed in his wake. "I just got up there and started dancing with Dylan, but no one else followed," she said. Was she embarrassed? She flushed: "Oh no. It was brilliant."

Such thrills are getting rarer. At 55, Bob Dylan's stock is low for a legend. Unlike the Beatles and the Rolling Stones and his other surviving Sixties peers, he has not had a Top 40 single in Britain since 1978, and only one hit album (Oh Mercy, in 1989). His concerts usually take place in theatres, not stadiums.

More importantly perhaps, for a singer famously concerned with the art of a verse before raw popularity, Dylan's river of work has shrunk from its mid-Sixties flood, first to a lazy meander and then, latterly, to a bare trickle. During the Eighties he wrote mostly poor, predictable songs; this decade, he seems to have hardly written at all, releasing albums of out-takes, old hits, old standards, live performances - anything but a set of new tunes like he used to gush out in a few months in his great years.

And the Dylan worldview, once enough to turn young minds in a line or two, has coarsened from rebellion to an insular misanthropy. "Everything is chaos," he concluded in a recent interview; his last album was simply called World Gone Wrong.

It is a message an ever narrower group of people want to hear. "My students don't drop Dylan into conversation the way they do the Stones and the Who," says Andy Blake, a lecturer in cultural studies at the University of East London. Across Soho from Helter Skelter, Dylan albums had been marked down to pounds 4.99 at Selectadisc, the area's largest specialist record shop. Students and teenagers rattled through CD racks of jungle, trip- hop, house, post-rock and all the varieties of modern pop music. No one went near the Dylan.

Radio stations have grown cool too. At Radio One, now redirected at a younger audience, his birthday on 24 May was marked by two Dylan cover versions and only a single original. Commercial stations playing older music are little friendlier: Dylan's nasal whine may be the right vintage, but it tends to divide listeners. Programme makers, anxious not to lose advertising, have taken note.

"He's not a core artist," says Trevor White, head of music at Virgin 1215. Dylan is lucky to be played once a day: "Artists like Dylan are used as an occasional historical thing. They are not selling records like they used to. Their recent work is not up to standard, so we tend to play the older work."

And Dylan's "older work" is growing distant. "Blowin' In The Wind" was written in 1962, when he was a skinny 21; "Like A Rolling Stone" started to form on scraps of paper in New York coffee houses only a year later. Blood On The Tracks, often said to be his last great album, came out in 1974. Scraps of brilliance sustained his audience for another decade, then, in the mid-Eighties, his fanbase began to fall away in chunks. Dylan was mangling his songs in concert, making clumping, empty rock in the studio, even agreeing to play a washed-out singer in a shell of a film called Hearts Of Fire. In 1987 it lasted a week in London cinemas.

That may have been the nadir. Another, which former fans tend to cite, was a song called "Wiggle Wiggle", which opened his last album of new songs in 1990. Since then, nothing on his records has been as embarrassing, but Dylan has busily erred in other ways. His trousers have been tight and his hair bouffant. "The Times They Are A-Changin' ", his insurrectionary anthem, has been sold to Coopers & Lybrand, a firm of accountants, for a television commercial. His headlong flight from his reputation continues.

Oddly though, all this seemed to have gone unnoticed at Helter Skelter. "Dylan still maintains his dignity," said Chris Whithurst with a straight face. The shelves behind him held yards of Dylan fanzines, like Isis and, indeed, Dignity, each grey with closely-typed analyses of the latest concerts and bootlegs.

Variation in performance - what non-believers would call inconsistency or error - is in fact the Dylan fan's lifeblood. Local Dylan groups meet in pubs to discuss differing studio takes; biographers feud over access to rehearsal tapes, discographers expose each other's inaccuracies over never-released songs.

Friday evening's centrepiece was a reading from the latest book on Dylan, a lovingly-detailed "sessionography" dissecting his every recording stint called Dylan Behind Closed Doors. Its author, Clinton Heylin, had put on pointed shoes and a striped shirt for his performance, just like Dylan circa 1965.

He stepped up on to themakeshift stage. "How many reviewers complain that the live version of a Dylan song doesn't sound like the record?", he asked.Wry smiles flicked round the room. "God help us," said Heylin. Smiles became laughter.

He read out a short chapter about a Dylan "pearl" called "Caribbean Wind", which had been lost, he said, by its writer's incessant revisions. Then, with a ghost of a smirk, he walked across the stage to a CD player and pressed play.

First came a rough strumming, then a few curls of electric guitar, then the voice, thick and quavering, edged with hiss but filling the room. Early drinkers clattered past outside; no one looked up. Foreheads rested on fists, eyes slipped out of focus, feet did not dare tap beneath plastic chairs. Heylin stood reverentially still, head slightly bowed, as if taking a service.

Six minutes wandered by in a trance. When it broke, they queued for their signed copies of his book in near silence, all earlier chat forgotten. Bob has his disciples still.