This is rock'n'roll central - a penthouse office festooned with the relics of a classic band: platinum discs, signed posters, original album artworks and tour-bus photos cover the walls. On a stuffed leather sofa sits The Who's iconic frontman, Roger Daltrey, his compact frame taut with energy as he holds forth . . . about teenage cancer, running a gym, shunning drugs, country walking and the day homoeopathy saved his baby's life.

Daltrey, 64, is the veteran embodiment of a wasted era, surviving days and ways that left many wild guys in bodybags or asylums. But the former sheet-metal worker who sang of sex, drugs, gender-bending - and My Generation's notorious anthemic line, “Hope I die before I get old”, has always been staunch about health and fitness. Nowadays this passion drives his energetic support for the Teenage Cancer Trust, a charity that builds specially designed units for NHS hospitals where adolescents can face life-threatening illness in surroundings so welcoming, supportive and familiar that it may significantly boost their survival rates.

The charity staged its high-profile annual event last month; six days of fundraising concerts at the Albert Hall including generation-spanning music from the likes of Madness and the Fratellis. But now, behind the glamour, the serious hard work starts again - building five new units this year, to add to the five that already exist. It has to be done in the face of an often obstructive health service, says Daltrey, his laser-blue gaze fixed with frustration. “There are so many hurdles to jump to get everyone to accept that they need a teenage cancer unit. The people in the hierarchies, everyone's fighting their corner. It seems that they can lose sight of the patients; the people become numbers.

“It takes from three to five years to get through the bureaucracy and get one unit installed. By the time we've done that the bloody price has doubled. Ridiculous!” He throws up his arms and laughs loudly, flashing his pearlies in a toothpaste-ad smile.

He's in great nick for a 64-year-old

The first impression of Daltrey has to be his height (5ft 6-ish), but it's quickly displaced by his room-filling expansiveness - a wide-open cocksure affability with just a shard of don't-mess, like a friendly clap on the back from a Kray twin. He's looking tanned, fit and in better nick than his fellow 64-year-old rock stars, Mick Jagger and Keith Richards (well, OK, everyone looks better than Richards).

He's also constantly animated, sitting back and forward on the sofa as he pushes the cancer trust's case. “It's not thinking about how to deal with medical issues - the hospitals' clinical staff do that. We provide an environment that is fitted to the people that enter it.

“Through that alone, we are getting a 15 per cent to 20 per cent improvement in outcomes. That's the psychological impact of how you treat a patient. If you could offer the NHS a drug that had a 20 per cent improvement in survival rates, they would throw money all over you. But it's a drug-related culture, and they don't appreciate the environmental approach we are taking. We let the teenagers do the designing. It has to be designed so that the clinicians can work, but the teenagers come up with the things that they want. The décor, we let them do it. They're the experts. It's amazing how much having a kitchen means to them, cooking their own food, and having their own dayroom. They can stay up all night - there aren't all these rules. We try to give these kids a positive experience of hospital.”

Daltrey's family doctor started the charity, but eight years ago he stepped in to give serious help when he realised that some stardust could boost the vital fundraising profile. “I thought, ‘Get out there, Roger, do it'.”

Surely though, the motivation to help teenagers must go deeper? Public introspection doesn't sit easily with Daltrey's eternal-geezer outlook, but he's willing to give it a go: “I've had cancer in my family, but it's nothing to do with that. I look at my life, I've been so privileged, I've won the lottery every day, making music and being paid to do it. Without teenagers back then, it would never have happened. They were there for me, now I'm there for them.”

I wonder if he's had any health scares himself. He shrugs. “My health's good. I have stomach problems, but I manage them. I swallowed a nail when I was 4 and had to have it surgically removed. The operating techniques were very basic. My dad and I were playing a little game, ‘Hide the nail', and I thought, ‘I'll get him'. So I ate the nail. The surgery caused a lot of scarring.” How does he manage his stomach problems? “Alternative medicines. Oh, you name it, I've done it. My experience of alternative medicines is that they all work for certain people. You are unique and you have to find the right thing for you. But, of course, alternative therapy is up against huge vested interests.”

What got him into complementary therapies? He gazes into his palms, then says: “I had a very, very dramatic experience with my son when he was nine months old. He had gastro difficulties, started throwing up, could not keep any food down and turned into skin and bone. At the hospital, they did every test to him, and in the end they just handed him back to me. My wife and I were in bits. My poor baby. The kid was dying. It was terrifying. I thought, there's got to be something. I'd heard of homoeopathy, so I found a local guy in the Yellow Pages and took my boy there. He gave him some powders. Within two weeks he was putting weight on, keeping the food down. The trouble recurred periodically for a couple of years, but he's now 27, a fit and healthy young man.

“The bizarre thing is that I've got a chiropractor friend in LA whose baby landed up in exactly the same state. He thought he was about to lose him. But I recommended homoeopathic remedies, and he recovered too. That's God's honest truth. Now I bet doctors would say, ‘Oh they'd have got better anyway'. But I can't believe that.”

Daltrey has long harboured other health interests. As one of the original 1960s open-shirt rock shouters, he made a career of flashing his honed pecs and abs. He's still whip-tight now. But asked about his fitness regime, he claims: “I'm pretty lazy. I used to run and I used to do a few light weights. But what made me fit was the stage shows. Those early Who shows were like intense aerobic sessions. You don't have to diet if you're doing that.”

Hmm, but didn't he open one of Britain's first ever lifestyle-friendly gyms - a far cry from the old-school macho sweatboxes that still dominated in the Seventies? “Oh, the gym - that was a waste of bloody money. I'm not a good businessman,” he laughs. “Gyms were taking off in America. They were wonderfully social. There are not many social things to do in England, apart from the pub. I thought, ‘This is something that could really take off.' Sadly, it was hard to inspire people to pay money to stay fit. The NHS does great things but it has created a psychology where people think that healthiness is, and should be, free. It ain't, mate. We're all paying an arm and a leg in taxes. People kind of think that their bodies aren't their business, that the NHS should pay for maintaining them.”

Health-freak rock'n'roller

Daltrey was also ahead of his time in being a health-freak rock'n'roller, which is undoubtedly why he is one of The Who's two original surviving members. The drummer Keith Moon died in 1978 after overdosing on Herminevrin, prescribed to help the symptoms of alcoholism, and the bassist John Entwistle died in 2002 of a heart attack in which cocaine was a factor.

Daltrey's refusal to binge on drugs, though, often meant cutting a solitary figure on the hedonistic tour circuit. “I did try some of the drugs, but singers need to be incredibly fit. I wanted to be a good singer, and I could not do it with drugs inside me. It was lonely, especially through the cocaine snowstorm that was the 1980s. All around me, people's personalities were changing. And everyone becomes incredibly dull on cocaine.” But then, Daltrey has always considered himself an outsider. “From early on I saw the tribe of rock'n'roll as silly, because no one was being an individual. It was too easy to be a part of that. I wanted to be more, to do it on my own terms, rather than doing what you were supposed to do.”

It helped, too, that he left the whirl of London to live a stable country life with his family in Sussex. “I was lucky in the 1970s to move out to a place where I had space for my head - and I found the highest high out there. I always loved space. I must have been 4 years old, playing on the bombsites in London, but I called it ‘running away to the country'. Now I love walking on the Sussex Weald. People think the South is crowded, but if you go walking around there, you see views and views and views.”

Daltrey's been married to his second wife, Heather (mother to four of his children), for 37 years. There's no secret to the relationship's success, he says. “It's my wife. She puts up with me. People aren't supposed to be married that long, but she's an angel. So it's easy. I've not been any model husband” - he casts around the room, at the floor - “I've always been open about our relationship. But I'm very proud and happy to be still together. I still look at women.” He bursts into laughter. “Yeah, I still admire a well-turned ankle. But that's the bloke in me.”

What about his other long-term relationship, with The Who's guitarist Pete Townshend? Does he fret about his fellow survivor's wellbeing? “Nah, he has an incredibly strong constitution. Despite all the stories about acrimony, we do get on very well. It's a very affectionate relationship. We've been working together for 45 years now, so don't ever try to get between us. But we have got completely separate heads. The band is my life and it is all I ever wanted out of my career. For Pete, it's just a section of his work, so there's two different agendas.”

No thoughts of retirement, then? “My voice is better than ever. I've got more control with it and I can do more things,” he says, entirely untroubled by self-doubt. “At my age I can start to do things on my terms. I need to keep going.”

The interview's drawing to a close, so I risk asking something that may just vex Daltrey beyond endurance. Doesn't he get riled by journalists constantly quoting, “Hope I die before I get old” at him in the light of the band's deaths, his work with teenage cancer and his own advancing years? “What?” he says, bolt upright. “No!” Then he relaxes. “I still believe those words. It depends how you define ‘age'. Some of the youngest people I've met are not young in years, but young in their mind. And I've met some really old 25-year-olds. It's about people who've kept their souls - it is a spiritual thing. I will go on singing that line - and f*** anyone who disagrees!”

For more information about the Teenage Cancer Trust, visit www.teenagecancertrust.org/

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