In an outtake over the credits, Ian McKellen jokes that this documentary about his life, career and LGBT activism is a bit of an obituary. As it happens he’s already sorted out his funeral. “Well,” he says, with a waggle of one of those owlish eyebrows, “I had an evening to spare … the most enjoyable evening.”

I can’t think of anyone I’d rather spend 90 minutes listening to than the subject of Joe Stephenson’s film. The format is simple: an audience with Sir Ian beefed up by archive footage and dramatised scenes of his childhood (beautifully acted by 15-year-old Milo Parker). McKellen occasionally slips into the part of twinkly super-cool gay uncle that he tends to play in interviews these days. But mostly he’s thoughtful and self-reflective (and not at all gossipy about his theatrical chums, disappointingly).

What we essentially get here is a profile of his success. McKellen believes that his drive to make it as an actor came as a boy from having to repress his true self as gay – at a time when homosexuality was illegal and impossible to talk about. He speaks about his mother’s death when he was 12 from breast cancer.

McKellen came out in his 40s during the Aids crisis and campaigned against the Conservative government’s vicious anti-gay Section 28. In archive we see him take down an establishment duffer with a killer combination of charm and cold, hard facts.

The thrilling clips here of his big Shakespearean roles are worth the price of a ticket alone. He says the luckiest thing that ever happened to him was becoming a film actor in the late afternoon of his career. About his film work, he calls Gandalf “a show-off” and there’s cracking footage of him being witheringly polite to Peter Jackson who’s giving him bland direction. I would have loved a few more probing questions.