In the mid-1960s, Kit Lambert and Chris Stamp were working low-level jobs at the Shepperton film studios outside London. Infected by the restlessness of the times and by their own youthful ambition, they came up with an inspired idea for a movie. It would be a cross between a documentary and an art project, tracing the rise of a rock ’n’ roll band. They would manage the group and record its exploits on camera, but the music would be a sidebar. The movie would be a masterpiece.

‘Lambert & Stamp’ Rated: R Opens Friday at Kahala 8

Things didn’t work out quite according to plan. There wasn’t really a movie. There was, however, a band, a scruffy foursome called the High Numbers, recruited from a London nightclub and renamed The Who. Maybe you’ve heard of them.

“Lambert & Stamp,” a loving, freewheeling new documentary by James D. Cooper, tells this origin story with panache and nostalgia. While it hardly slights the achievements of the musicians — notably Pete Townshend, the band’s guitarist and principal songwriter, who appears on camera as an angry young man in concert footage and as a wise elder statesman in present-day interviews — the film dwells on the improbable partnership behind their success. It is, above all, a portrait of two friends seizing the creative and business opportunities available to their generation.

Stamp, his hair a little grayer than it was in 1967 but just as shaggy, appears in interviews as a genial, energetic raconteur. (He died in 2012.) The younger brother of actor Terence Stamp (who shows up to add some background details and an extra dash of ’60s British outlaw cool), he grew up in the rough, striving milieu of the postwar English working class. He and his partner were a classic chalk-and-cheese pairing. Lambert’s background is repeatedly and succinctly evoked by the word “posh.” The product of elite schooling and Oxford University, he spoke in the plummy accents of the British ruling class.

Lambert comes across as a complicated, sometimes contradictory character. He was highly cultured and wildly rebellious, a pop genius who happened to be the son of a well-known classical composer and conductor. He was openly gay when sexual liberation was still largely the prerogative of heterosexual men in a country where homosexual activity was still a crime. His creative gifts were best realized in service of the talents of others, most notably Townshend, whose growing confidence as an artist owed much to the man who was his friend, producer, collaborator and sometime rival.

Sadly, Lambert is not around to tell his own version of the story. He died in 1981 after struggling for years with mental illness and drug addiction. His is not the only tragedy casting a shadow over the film’s exuberance. Keith Moon, The Who’s drummer, died of a drug overdose in 1978. John Entwistle, the bassist and resident musical prodigy, died in 2002. “Lambert & Stamp” is in effect the tale of six men, only three of whom survived long enough to tell it here.

Their eloquence and generosity help overcome the limitations imposed by mortality. Roger Daltrey, the lead singer, is modest and candid in recounting the ambiguities of his role as charismatic frontman and second banana. Along with Stamp and Townshend, Richard Barnes, known as Barney — a friend and follower in the early days — supplies vivid recollections of late-’60s London. There is enough archival footage to make you feel as if you were there, or at least sorry that you missed it all.