Like a group basking in the success of a hit record, Hipgnosis were suddenly in demand. In May 1973, Marshall Chess, the president of Rolling Stones Records, requested a meeting. Hipgnosis had met Mick Jagger when he visited Egerton Court. Since then, the Stones had made a run of great gnarly rock’n’ roll albums – Let It Bleed, Sticky Fingers, Exile on Main Street – and now drifted around the globe like gypsies in a tax-exile bubble.

Storm and Po were summoned to guitarist Keith Richards’ flat in Cheyne Walk and given an album title, Goats Head Soup. Within days, they’d dreamed up a concept: the Rolling Stones as mythical centaurs and satyrs in a woodland glade.

‘Pre-Photoshop, that was some feat,’ admits Po. But if any Stone lent himself to a pair of cloven hooves, it was Richards. Hipgnosis explained that the group would be photographed wearing ballet tights; a blank canvas onto which the animal limbs could be grafted later. ‘The Stones said, “Great, yeah, yeah, fine,”’ remembers Po. ‘They wanted this.’

Hipgnosis shot many musicians at Denmark Street but chose Bow Street Studios in Covent Garden for the Stones. They shipped in food, beer, a music system, ballet tights from Anello & Davide and a television set in case Jagger wanted to watch the cricket.

Hipgnosis’s friend and photographer, Alex Henderson, worked at Bow Street and attended the shoot. Most of the Stones arrived after midday, but hours later, there was still no sign of Keith Richards. ‘Unfortunately, Keith didn’t turn up until seven o’clock in the evening,’ says Henderson. ‘This didn’t surprise me, as I’d seen him, out of his brain on Portobello Road, at 4 a.m.’

‘Richards was in a foul mood when he arrived,’ adds Po, ‘and that set the others off, because they were pissed off he was late. So, suddenly they were all in a bad mood.’ Especially bass guitarist Bill Wyman, who’d been reluctant to dress up anyway and was now scowling in a pair of figure-hugging tights.

Sandwiches and beer couldn’t lighten the mood. ‘So we sent out for a bottle of Jack Daniel’s and a gram of cocaine,’ says Henderson. ‘Once they arrived, Keith’s mood changed. Suddenly, it’s, “Yeah, man, this is a great idea,” and he really got into wearing those tights.”’

In the subsequent photos, Jagger and Richards resembled a pair of rock ’n’ roll Nijinksys and even Bill Wyman cracked a smile. A maquette was created, showing the bare-chested Stones as centaurs, and Hipgnosis agreed to deliver the finished artwork in three weeks. Then, just before deadline, came an urgent call from Marshall Chess: the Stones had changed their minds and Hipgnosis should stop immediately.

David Bailey had photographed the group after them, and Jagger was very taken with Bailey’s shot of himself wearing a chiffon veil and wanted it for the cover instead, because, it reminded him of Katharine Hepburn’s character in The African Queen.

‘We were upset and angry, and we didn’t get paid,’ grumbles Po. ‘Very rarely did we do work on spec, but it was the Stones so we had no reason to think we wouldn’t get the job. It was our biggest disappointment of the decade.’

Hipgnosis stuffed the negatives in an envelope, sealed it with Gaffer tape and threw it into a cupboard. It was the album cover that got away and the envelope remained unopened until after Storm Thorgerson’s death.

Goats Head Soup was released that summer with a chiffon-draped Mick Jagger on the sleeve. Alex Henderson was singularly unimpressed: ‘That cover was shit.”