Leaving aside for a moment the issue of whether an unshown TV special from ’68 could capture, as the opening credits suggest, “the spontaneity, aspirations and communal spirit of an entire era” any more accurately than, say, Catweazle or Do Not Adjust Your Set, and regardless of whether you think Beggars Banquet and Let It Bleed are the fulcrum points of a generation or just something that music critics of a certain age should learn to get over, the portents of this cryogenically preserved moment in rock time are undeniable. Look! There’s Brian Jones in his twilight; puffy-faced, baggy-eyed, pilled and paunchy, just months from death. There’s Keith Richards’ priceless flicker of polite disdain when Yoko gets up on stage to wail along with hubby and heavy friends. There’s Lennon himself, caught at the precise moment he stopped writing songs about acid-ennui and started writing them about smack-ennui instead. And at the centre of it all there’s ringmaster Jagger, presiding over proceedings in his best gorblimey-gargled-in-mandrax accent, and staying focused-focused-focused for 36 hours until it’s all done and in the can. Which, of course, is where it remains for nearly 28 years until lan Stewart’s widow cleans out the shed one day and blows the dust off a vital historical document.

The guests run the full gamut from Bagism to Dragism. The opening spot went to Jethro Tull. It was their first big break and they grasped the opportunity with both hands. The name lan Anderson was often exhaled in the same breath as Roland Kirk at the time, and he proved to be as adept a showman as Kirk, too. In fact, with all that eye-rolling, lip-licking, gurning, long john silverism, the Tull frontman, for all his underground status, was as shrewd a manipulator of image as any manufactured bubblegum act of the period. Heard in short bursts, the Tull’s rambunctious jazz Bach’n’boogie has aged surprisingly well.

Next comes the highlight of the show. The Who’s splenetic, intense performance of “A Quick One” was allegedly the reason Rock And Roll Circus sat in the vaults for so long. And it’s undeniable that Pete Townshend’s first erratic truncated try-out at a rock opera grabs the glory. He’s touchingly self-effacing about it all in the DVD interview, but there’s nothing here to dispel the notion that The Who blew the Stones off the stage.

After Taj Mahal’s routine barroom R&B comes Marianne Faithfull. Already wearing the ravages of lost innocence in the cracked voice and the dulled belladonna gaze, she turns in the most beautiful performance of the entire event. Resplendent in a black crepe dress and displayed centre-ring like a lonely ice figurine on a giant cake, she performs her version of Mann-Goffin’s “Something Better”, probably the second best social conscience song to come out of the Brill Building after Carole King’s “The Road To Nowhere”. Which would have been an equally appropriate choice given what lay ahead.

After the obligatory Brit-hippie exotica from model Donyale Luna, all throbbing bongos and writhing flesh (very Powis Sq), Messrs Clapton, Lennon and Richards, aka Dirty Mac, do their supersession bit. The pernicious, tangible influence of king heroin once again hangs like an LA fog over proceedings. Great version of “Yer Blues”, though.

Which brings us to the hosts. Clearly this isn’t the Stones’ best ever live performance. Jagger’s intros and interjections are frequently forced and uninspired. A perfunctory “Jumpin’ Jack Flash” just about reaches something approaching urgency by the final verse. The rendition of “Parachute Woman” is equally so-so. Thankfully, things pick up a bit after that. Brian Jones manages some delicate slide work on “No Expectations”, and Jagger’s flirting, taunting interaction with the girls in the front row finally comes alive. “You cannot always get the man that you want honey,” he teases, as the girls wear their best “Ooh, isn’t he awful” demeanors. Meanwhile Jones throws gallows shapes. On “You Can’t Always Get What You Want” he sounds like he’s had his amp turned down. On “Sympathy For The Devil” he’s reduced to rattling maracas. From founder member and seeker of the holy Delta grail to proto-Bez in just five years.

It all ends with a mass sway-along to “Salt Of The Earth”. Altamont is just a shot away.