Quite a few of Townshend's peers duly went on to make premature exits, but those rockers who survived are now firmly entrenched in middle-middle-age and not quite sure about the dignity of their survival. Or, as Townshend puts it: 'One of the perennial problems for people like me who are growing old in rock'n'roll is the idea that age has something to do with the process. Age obviously has a lot to do with performing rock'n'roll, because you become the troll when what you really want to be is the beautiful princess. You become one of the villains . . . you become less neutral as a storyteller.'
This year, Townshend has tried to cope with the dilemma of growing grizzled in an arena obsessed with youth by telling three different stories about three different ages of man. He has re-embraced one of the most burdensome creations of his young adulthood by taking a new version of Tommy to Broadway, and has been rewarded by great box office, heartening notices and no fewer than five Tony awards. He has pondered the miseries of the balding troll in Psychoderelict, an album-cum-audio-play about a battered pop star from the Sixties who can't stop wondering what happened to 'all that lovely hippy shit'.
Finally, he is going back to the world of pre-pubescence with The Iron Man, a rock musical based on the children's book by Ted Hughes, and staged by London's Young Vic under the direction of David Thacker. The poet laureate has been giving Townshend advice over the phone, and is rumoured to have been reduced to tears (of the deeply moved rather than the utterly horrified kind) by what he saw when he attended a rehearsal.
For many outsiders, the prospect of a hybrid offspring from the writer of Wodwo and the composer of Quadrophenia might appear rather incongruous, if not downright freakish. (Swift caricature: an amphetamine-crazed mod teams up with a killer crow and trashes Brighton . . .) But Townshend - a mild, garrulous, altogether affable character these days - says that The Iron Man has proved eminently suitable material for his purposes, since he believes that there is a strong affinity between the mythology of rock music and the plots of classic fairy tales.
'In rock'n'roll there's this place,' he suggests during a lunch break from rehearsals, 'this space between childhood and adulthood where you're acutely aware of being alone for the first time - you're not necessarily lonely, but when you decide to leave home you're alone, and you can never go back. That's what rock'n'roll addresses, that moment. I think it may have originated in a scene with James Dean in East of Eden, or in a scene in Citizen Kane. Rock'n'roll in the white sense came from there, as well as from black R & B and from Elvis Presley.
''I felt that the best children's stories were all about that moment being anticipated by younger kids. The Iron Man is definitely about that, it's a story that Ted wrote to his kids to say, listen, pretty soon you're going to have to grow up. Ted wrote me a letter saying that the function of the book was to empower his children - I think that's the word he used, (mock- American talk show accent) a kinda Oprah Winfrey type word - to show them that your imagination is a supremely powerful instrument.'
Hughes's fable, to which both Townshend and Thacker say they have been faithful in almost every respect, is about a mechanical monster which terrorises the countryside until it is foiled by a lad called Hogarth, who then calls on its powers to defeat a menacing dragon from outer space. Townshend's interest in the tale began as long ago as 1976, when he was trying to run his own publishing company specialising in children's books, and his partner showed him Iron Man as an aspirational model. (Matthew Evans of Faber was impressed by their efforts, and invited Townshend to join the old firm as a consultant - 'So it was Iron Man which got me my job at Faber'.)
Work on a musical treatment of Iron Man eventually resulted in what Townshend describes as a 'demo' album, which was released in 1989 and promptly vanished. The stage show, with its greatly revised and expanded score, dates from last year, when David Thacker approached Townshend about the rights for Tommy, discovered they had already gone to Broadway, and sat down with the rocker to see what could be done. Two main changes took place. To start with, Hogarth, the little boy, was brought closer to centre stage. Hughes was happy enough about that, but had his doubts about the other alteration.
'The only thing we're still fighting about was that it was my absolute requirement that there be a woman in the piece because musicals are always about relationships - there were even women in La Cage aux Folles] I came to a rather impudent assertion that the Space Dragon is a woman, and the book is actually about a man and a woman and their child - with the Space Dragon and the Iron Man fighting and the child in the middle looking up, it really evokes . . . '
Mum and Dad rowing? 'Yeah. The things I used to get when I was a child, the cups flying. Not the fear or the distress of it, not even the fear of there being a break-up, but the fear of being excluded from the excitement . . . ' And so The Iron Man has become another telling of the Townshend plot which underlies all the others: the one about 'the boy in the dysfunctional family, or the dysfunctional boy in the functioning family'.
He hopes that the show will break out of the impasse he dramatised in Psychoderelict, and manage to reach the children of the Nineties in the same way that his first singles affected the adolescents of the Sixties, some of whom have kept their faith with the music of The Who and the confusion it expressed: 'I still see some of the people who came backstage to talk to us back in the days when I was something like the artist in residence for the expatriate Irish community in Shepherd's Bush. I partly based Quadrophenia on one of them, a boy called Irish Jack. He turns 50 today]' In other words, The Iron Man tries to offer a sombre twist on the sickly kiddy-show cliche: it's for children of all ages.
'The Iron Man' opens at the Young Vic on Thursday (Box office: 071 620 0568)