The writer Jack Rosenthal once put his inability to get to grips with a biopic of Charlie Chaplin down to the fact that Chaplin’s life was ‘all highlights’. A similar problem besets BECOMING CARY GRANT, of embarras de richesse: not only is there a cache of home movies to back up the known and recorded details of Grant’s four decades as a star, there’s also the startling discovery thathe spent time during the 1950s under the (legally prescribed) influence of LSD. What’s more Grant wrote up his reactions to this form of psychotherapy together with his innermost thoughts about having an identity crisis in a memoir, extracts from which are sympathetically read by Jonathan Pryce.

The story of how young Archie Leach from the back streets of Bristol became the byword for Hollywood sophistication is extraordinary already, even before these ‘bonus extras’. After his depressive mother Elsie disappeared from the family home before Archie was ten (his father had her committed to an asylum and it was another twenty years until he saw her again) he joined a travelling acrobatic troupe while still a teenager and moved with them to New York, eventually playing a series of good-looking but stolid leading men first on Broadway then in Hollywood, where he took the name Cary Grant.

After half-a-dozen or so nondescript roles he was cast opposite Mae West and Katharine Hepburn as leading directors like George Cukor SYLVIA SCARLETT), Leo McCarey (THE AWFUL TRUTH) and then Howard Hawks (BRINGING UP BABY) started to exploit Grant’s comic potential, not least with an acrobatic pratfall. After a comedy tour-de-force in Hawks’s HIS GIRL FRIDAY (not mentioned in the documentary) it was Alfred Hitchcock who started to bring out Grant’s darker side in the thrillers SUSPICION and NOTORIOUS, before helping buff up his suave leading man image in the glossy romantic thrillers TO CATCH A THIEF and NORTH BY NORTHWEST.

But Cary Grant was never quite able to leave his past behind: in the bleak NONE BUT THE LONELY HEART (1944) he plays a Cockney semi-criminal under the thumb of a domineering invalid ‘Ma’ (Ethel Barrymore) – on the wall of the set is a picture of Grant’s own errant father. As the home movies show, Grant never abandoned his mother and paid for her care in Bristol, while visiting her periodically with his latest wife, five of them in all. It was Number 3, Betsy Drake who had introduced Grant to the LSD treatment which he undertook at the height of his fame as Hollywood’s most successful leading man.

Sadly, with this wealth of material to hand, BECOMING CARY GRANT simultaneously offers too much and not enough information in what becomes a muddled piece of work: his lengthy and fascinating relationship with rugged Randolph Scott – pictured enjoying domestic bliss in the likes of ‘Hollywood Babylon’ – is never mentioned, and while reconstructions of Grant on the couch in the psychiatrist’s office as he hallucinates are fair enough, linking his existential crisis to a clip of the ‘crop-dusting’ scene in NORTH BY NORTHWEST tends towards the crass. The best and most straightforward analysis of Grant’s enigmatic life and career comes from the film historian David Thomson, and there is touching testimony from his fifth wife Barbara Jaynes and daughter Jennifer about his long years in retirement.

So a target missed: though maybe the confusion of style and content makes the documentary truer to its subject – Cary Grant never really knew who he was either.