These days, Aubrey Powell is a genial 70-year-old who can be found most mornings having breakfast at his local Knightsbridge café. But in the late 1970s, he did something that surely no other human being has done before or since. He photographed a sheep lying on a psychiatrist’s couch on a beach in Hawaii. Its coat had been treated with Vidal Sassoon products, and it was sedated with Valium because it was scared of waves.

So what on earth was he up to? The answer — as anybody who recognises Powell’s name will guess — was creating one of the 373 album covers that his company Hipgnosis designed back when LPs ruled the world. (In this case, for 10cc’s Look Hear?)

Now Powell — known as Po — has gathered all 373 together for the first time, in a book that for some of us thrillingly recalls those many happy hours spent flipping through album racks in record shops. Po’s accompanying commentary does acknowledge the occasional misstep. (‘An embarrassment to the Hipgnosis catalogue,’ he writes of one particularly dodgy schoolgirl-based sleeve.) Nonetheless, what’s most striking is how endlessly inventive yet consistently dazzling Hipgnosis covers were: not just the famous ones for the likes of Pink Floyd and Led Zeppelin, but also those for, well, virtually every 1970s rock band you can think of — and plenty that you probably can’t.

Having joined Po in that Knightsbridge café at the decidedly non-rock’n’roll hour of 9 a.m., I ask him what it was like seeing Hipgnosis’s work collected together. Did it create in him the feeling Paul McCartney (another former client) often seems to have: that of a man who can’t quite believe what he achieved in his younger days?

‘I did have a sense of that,’ he says with what proves to be characteristically understated pride. But there was also the sadness that comes with being reminded of a world, and of some much-loved colleagues, now gone.

One colleague there from the start was Storm Thorgerson, who he met in an archetypal 1960s way. In 1966, Po was a 19-year-old former public schoolboy living in Cambridge when he decided to call on some local bohemians he liked the look of. Barely was he through the door than Storm welcomed him with a cheery ‘Hello, man, want a spliff?’

Po did — and from there, his ascent into 1960s bohemia was almost eerily smooth. Among those Cambridge hippies were Pink Floyd and at an early gig of theirs at London’s UFO club Po shared a joint with Paul McCartney and Pete Townshend. The band also commissioned Storm and Po’s first album cover — for A Saucerful of Secrets — which naturally drew on Tarot cards and the I Ching.

Less happily, Po witnessed the sudden LSD-fuelled decline of Pink Floyd’s former leader Syd Barrett, with whom he shared a London flat. ‘It happened over a weekend. On Friday he was Syd: a beautiful, charming, very bright man. By Monday, he was gone, burnt out. We’d been best buddies, but his personality flipped to being extremely aggressive, smashing things up, burning his girlfriend with cigarettes. He was very scary to be around.’

But one inadvertently useful thing that Syd did do in the flat was write the mysterious word ‘Hipgnosis’ in Biro on a white door. Adopting it as their name, Storm and Po moved into an office in Soho to establish a proper company. ‘Musicians were always stopping by for a chat,’ recalls Po, who was soon cast in the role of the company grown-up, with Storm as the eccentric ideas man. ‘It was great, but I sometimes did think, “For God’s sake fuck off, we’ve got work to do.”’

Hipgnosis’s breakthrough year was 1973, with Led Zeppelin’s Houses of the Holy, Wings’s Band on the Run and, most world-conqueringly of all, that white light going through a prism for Pink Floyd’s The Dark Side of the Moon. ‘After that, the phone didn’t stop ringing,’ says Po. ‘Suddenly we’d gone from amateur art-school studio to a pretty slick professional outfit.’

Their timing couldn’t have been better. By the mid-1970s, the music industry was awash with money — and willing to spend it. Not only could Po spend a week in Hawaii while someone made a psychiatrist’s couch for a sheep. (‘I could probably have done that photograph on Camber Sands,’ he admits with a chuckle.) He also got three months in a suite at the New York Plaza out of doing the cover for Led Zeppelin’s The Song Remains the Same.

Before long, he was living rather like a rock star himself, joining bands on their private jets and at those notorious 1970s post-gig parties (about which he’ll only say that ‘all the stories are true’). After being punched by Paul Rodgers of Bad Company for ‘drumming on a table out of tune’, he even drunkenly smashed up a hotel room, which, as far he remembers, was surprisingly good fun.

For Po, it duly seemed as if the golden age of albums, and album covers, would never end. In the event, if you date its birth — as he does — from Sgt Pepper in 1967, it lasted just 15 years, until the arrival of CDs in 1982.

Before that, though, Po had his first inkling of a less certain future when ‘some scruffy herberts’ called the Sex Pistols moved into a neighbouring studio. ‘I remember one of them wearing a T-shirt saying “I Hate Pink Floyd” and I thought times are changing. We were still playing Crosby, Stills and Nash and wearing velvet trousers.’ Even worse, ‘the brilliant cover’ of the Sex Pistols’ Never Mind the Bollocks ‘must have cost about 2p. Storm and I looked at each other and said, “You know what? The writing’s on the wall for our style.”’ Meanwhile, rumours were emerging of a new format that wouldn’t have room for proper cover art anyway…

And so, in 1982, Hipgnosis moved on to pop videos. Then, after falling out with Storm (a rift happily healed by the time of his death in 2013 by which time ‘we were like brothers again’), Po became the creative director for Paul McCartney’s world tours. He’s now in the extremely time-consuming process of curating the enormous Pink Floyd exhibition that opens at the V&A on 13 May.

Of all the rock stars Po’s known, the ones he appears to admire most are those who, like Roger Waters and Paul McCartney, have remained utterly driven. And the same, it seems, firmly applies to him. ‘I’m absolutely hammering it,’ he says contentedly, ‘14 hours a day, seven days a week and loving every minute. I never want to stop. Why would I?’