So much has been said about Spike Milligan that another documentary is unlikely to change the narrative of a tortured genius damaged by war and the demands of cranking out Goon Show after Goon Show single-handed.

However, Spike Milligan: The Unseen Archive certainly fleshed out the image, thanks to the access treasure trove of material the comedian carefully filed away over his lifetime. Even the fact that a man with such a turbulent mind maintained such meticulous records is a revelation in itself.

With current sensibilities, it can be hard to grasp just how revolutionary Milligan’s work was, although a very formal interview included here shows the rigidity of the broadcasting establishment that his anarchy challenged.

Unseen work projects, in script or video form, are one thing – but the personal effects are, of course more illuminating. It is heartbreaking to hear his voice on tape saying all the treatments he underwent for his bipolar disorder have been a failure. Meanwhile, the cartoons he sketched while in a psychiatric unit say so much about him maintaining his sense of humour at the worst times.

Interestingly, his children recall only happy times at home, even while the demands of the Goon Show were taking their toll. ‘Childlike’ is a word that cropped up frequently about Milligan himself, so no wonder he cherished the company of his offspring. Even they hadn’t seen the footage of Spike being interviewed with his own parents Leo and Florence. And who knew they were entertainers themselves, having a Wild West novelty act?

We also hear Spike’s poetic descriptions of his childhood in India, though being a child of Empire instilled some attitudes that haven’t held up so well. This film could never gloss over the racist tropes of shows like Curry And Chips, in which he blacked up to play a Pakistani – controversial even at the time – and didn’t.

Nor did the documentary overlook other failings of his career, that sometimes he could produce mediocre ‘that’ll do’ dross. But, as contributor David Quantock pointed out, there are more than enough works of genius to compensate.

In the years before he died in 2002, aged 83, Milligan felt undervalued by the BBC and struggled to get his work on air after his last Q series ended in 1982. He ascribed it to not being an Oxbridge graduate, and it clearly grated.

In the film, Milliganesque animations liven up the presentation of the material and interviews. And rather than the standard parade of talking heads being presented in isolation, celebrity fans such as Al Murray, Eddie Izzard and Ian Hislop are seen getting genuinely excited at laying their hands on items their comedy hero once owned. It can be no coincidence that all those involved already had a strong interest in history in general, so appreciate the value of primary sources.

And Spike Milligan: The Unseen Archive had an embarrassment of such riches, enabling it to achieve the seemingly impossible task of shedding new light on this one-of-a-kind comedic titan.

• Spike Milligan: The Unseen Archive aired on Sky Arts and is now available on demand and via the streaming service Now