The band dubbed by Rolling Stone magazine the Greatest Live Band Ever are back on the festival circuit that they helped to invent. The Who kick-started the festival experience back in the late 1960s when incendiary performances at Monterey, the Isle of Wight and Woodstock convinced a generation that being transported to rock Valhalla beat working for the man, at least until Monday morning.

The four decades of rock’n’roll that followed have claimed the lives of their drummer Keith Moon and bassist John Entwistle, not to mention the hearing of Pete Townshend. But The Who remains the ultimate rock band and Townshend’s adoption of on-stage ear protectors does nothing to alter that.

Yet touring rock stars need distraction. And where younger musicians might indulge in drugs, or groupies, Townshend has found a more original hobby. When The Who have a little downtime Townshend and his partner, Rachel Fuller, a classically trained pianist, have persuaded the likes of Bob Dylan and Lou Reed, as well as much younger artists, including the Kooks, the Fratellis, the Raconteurs and Martha Wainwright, to join them in a futuristic silver trailer equipped with recording equipment and webcam technology to perform impromptu songs together. Whatever comes of the meeting of musical minds, however good or bad, is broadcast live on Fuller’s website. The Attic Jam sessions have been a huge success, and given Townshend a new lease of life.

We’re at Oceanic Studios in Richmond, the recording hub and rehearsal room that Townshend built 30 years earlier. Fuller, 33, who has just given up cigarettes and has a Nicorette patch filling her with nervous energy, is not the type of woman to fit into a passive role as rock-star girlfriend. Sitting side by side in an office overlooking the Thames, Townshend and Fuller jostle for speaking space, interrupting each other, arguing and laughing as they explain how Attic Jam got started.

Fuller, getting in first, says: “The Attic was a music webcast that I began right here as a way to find an audience. But soon after I started it, The Who signed up to do a world tour. I knew that I didn’t want to be a rock-chick girlfriend following Pete around, so we fitted a caravan with a portable studio, found a guy that could link it up live via satellite, and took it out on the road. Then we just grabbed guests as and when we could to come in the caravan to jam.”

Townshend appears to have shaken off the surliness for which he was once known. Enthusiastic and cheerful, he’s eager to engage with the world, and you cannot help but suspect that his girlfriend of ten years has played a part in that. He has been eulogising the shared experience of festivals and democratising power of digital technology for decades, but a few nasty burns over the past few years (not least his caution for accessing a child pornography site on the internet, which he did as research for a book) have caused him to retreat from the public eye. His reemergence, and willingness to put himself on an equal level with musicians far younger and less famous than himself, is a pleasant surprise.

“The main problem with The Who is that I get bored,” says Townshend when he eventually gets a word in. “We’ve done 120 shows on the last tour alone and we’re doing roughly the same set every night. Over the course of my life I must have played Can’t Explain 5,000 times. What am I going to bring to it? For me, what’s been nice about Attic Jam is getting back to the spontaneity and freshness of playing songs for the first time.”

Fuller knows how he feels. For two years she worked as the resident organist at a crematorium and had to play The Lord Is My Shepherd an average of eight times a day. The only variety came when the undertakers allowed her to press the button that sent the coffin into the inferno during her lunch break. And even a musician of Townshend’s stature gets nervous at the spontaneity required of the Attic Jam sessions.

"When I go into that caravan during a festival, everything is being recorded live," he says. "I meet the artist there, usually for the first time, I have a quick look at the song they want to play, and suddenly I'm playing it. Even I don't know if it's going to be any good or not. The Fratellis gave me a chart of their song Cigarillo and we did it there and then. The Flaming Lips gave me a little toy guitar that I had to work out how to use. It's a challenge that I have to rise to."

Taking the Attic Jam on to the festival circuit has forced Townsend to learn new tricks. Because Keith Moon was a highly expressive drummer with an unconventional sense of timing it was left to Townshend (and Entwhistle) to hold the rhythm gogether during The Who's formative years. As a result his playing is in the main straightforward. For some of the Attic's visitors that just wasn't good enough.

The Who is mostly three-chord-wonder stuff, but some of the Attic live shows can be quite scary. The hardest was the one with Sean Lennon because his songs are filled with bossa-nova chords, and they’re complex. When we finished he said: ‘You’re the only musician who has got one of my songs first time.’ I felt so proud of myself at that moment.”

It’s nice to know that even rock legends can find reasons to pat themselves on the back.

While young performers such as Martha Wainwright and the Fratellis jumped at the chance of making impromptu music with the man who wrote My Generation, Pinball Wizard and Won’t Get Fooled Again, artists of Townshend’s own generation have been a little more reticent.

“When I’ve approached people such as Lou Reed,” he says, “the answer has always been: ‘Sounds interesting, but what are we going to do?’ Younger artists rock up to the trailer with a bottle of beer and a guitar and they don’t seem to give a damn about whether what comes out is good or bad.”

“People warned me that Lou Reed would be impossible to work with,” adds Fuller. “And OK, he doesn’t spring into the room like Pollyanna. But once he was playing with us, he enjoyed himself. Most people do.”

Despite surviving Reed, when Fuller suggested that they ask Bob Dylan, Townshend replied that she must be out of her mind. Not only would Dylan never agree, but Townshend was too in awe of him to ask. Fuller had no such qualms. “I’ve realised now that I mustn’t make a big thing of this stuff,” he says. “These people are just musicians. You show each other some chords and you play.”

The Attic Jam was Fuller’s idea, but it could well be Townshend who is getting the most out of it. One of the webcasts on intheattic. tv shows the rock god relegated to the role of session tea boy, and he doesn’t appear to be complaining. Sometimes Fuller’s irreverent approach to rock stardom proves too much for Townshend – he draws the line at joining the actor Jack Black in a comic medley of songs by The Who – but her initiative and encouragement has given him the energy a 63-year-old man needs to brave the festival circuit.

“If I do the Attic at a festival before a set by The Who I go on stage feeling rejuvenated and energised. And because it is on the internet, the Attic reflects an increasingly tribal musical climate in which the audience response guides the evolution of the thing. We're not tastemakers here. We're just responding to what’s going on around us.”

Fuller, as ever, is more pragmatic still about her motives. “It’s a bloody good laugh,” she says. Which, let’s face it, is the only decent reason for going to a festival at all.

The Who headline Glastonbury (page 26) and Knowsley Hall (page 26). Attic Jam: the Album is available from iTunes. intheattic.tv

Editor's choice

• U2 at Nou Camp Stadium, Barcelona
• The 50 Best Movie Villains
• The 15 golden rules of theatre etiquette