There’s a story Stanley Kubrick’s friends like to tell. On the set of Eyes Wide Shut, the renowned perfectionist had outdone himself.

In a scene where Sydney Pollack’s wealthy socialite addresses Tom Cruise’s doctor, the actors had been requested to go through the motions yet again. Pollack had been hired for three days’ work, but his tenure had already extended into a third week. They had performed the scene hundreds of times, covering every conceivable interpretation. Why on earth, Pollack asked, would the director possibly need it repeated? Quipped Kubrick: “Don’t you want to get it right?”

Jan Harlan laughs when recounting the tale. As Kubrick’s brother-in-law, the sibling of Kubrick’s widow, Christiane (both German-born), he knew the man, who died of a heart attack in March 1999, better than most. His documentary Stanley Kubrick: A Life in Pictures stands as the best of the filmed tributes.

In the late 1960s, as a businessman, Harlan had been brought in to negotiate the rights to Arthur Schnitzler’s Traumnovelle, the book on which Eyes Wide Shut was based. He ended up as executive producer on all Kubrick’s films from Barry Lyndon (1975) onward. “I didn’t know about films, other than going to the movies,” the 73-year-old shrugs. Such was Kubrick’s universe that those who served him well got sucked into his orbit, unable, usually unwilling, to resist.

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Another such was the film-maker Andrew Birkin, who began his career as a tea boy on 2001: A Space Odyssey. He demonstrated some precocious ingenuity in the art department, so Kubrick promoted him to “first assistant director, special effects”. Both men were to play key roles in a Kubrick project that has been hidden from public view for 40 years.

In recent times, there has been as much interest in the movies Kubrick didn’t make as those he did. His sci-fi film AI, conceived before the computer effects existed, was bequeathed to Steven Spielberg. The Aryan Papers, a film about the Holocaust that Kubrick, a Jew, had planned, was abandoned when it ran into competition with Schindler’s List.

Most intriguing of all, though, is Napoleon. A purported three-hour epic, it would, at a budget of $5.2m (about $100m today), have been the most expensive film of its time, shot in the UK, France and Romania. For 40 years, its content has been the subject of conjecture among film buffs; snippets of information leaked out about this unrealised “masterpiece”, but the critical material stayed under lock and key.

Just north of St Albans, in Hertfordshire, nestling in rolling countryside, the 120-acre Childwickbury estate is reason enough why Kubrick remained in England, making all his films here from 1962’s Lolita. He bought Childwickbury Manor as a leaky pile in 1978, its restoration a labour of love.

Today, in the hallway, the sinister masks from Eyes Wide Shut leer from the wall. Off the atrium, in which Christiane’s brightly coloured paintings hang, is the library, once a private screening room. Around the cavernous kitchen flit family members, still in residence, and cheery household staff. It was in the kitchen that Cruise and Nicole Kidman rehearsed. The big oak table is the one at which Jack Nicholson hammered out his “All work and no play” manuscript in The Shining, a prop from Pinewood. Cruise once landed his helicopter on the lawn, Harlan says. It frightened the dogs. (They roam freely, accorded the status of Hindu cows.) And there, across the grass, within a shady copse, rests the man himself, his presence still looming.

An outbuilding is now an Aladdin’s cave of boxes and flight cases, housing material from all his films. Original prints — labels reading “The Killing Reels 1-5”, “The Shining Reels 6-9” — lie jumbled. Harlan opens a safe and pulls out the heavy Zeiss lens, of Nasa specification, that enabled Kubrick to film scenes of Barry Lyndon by natural candlelight, one of numerous technical breakthroughs. And there, tantalisingly, sit those boxes marked “Napoleon”.

Some of their contents finally see the light of day this month, with the publication of a set of books entitled Stanley Kubrick’s Napoleon: The Greatest Movie Never Made, from Taschen. The title is a play on Kubrick’s own boast when touting the project for an intended 1972 or 1973 release. “Making a book about an unmade film is quite an unusual challenge,” says its editor, Alison Castle. The boxed set of volumes, featuring Kubrick’s 28,000-word “treatment”, transcripts of conversations with academics, the annotated screenplay, even pictures of finished prototype costumes, as well as sundry research materials, is a collation culled from 88 boxes — no mean feat, judging by the thousands of documents I saw exploding from one trunk alone.

Napoleon once remarked that his life would have “made a great novel”. “I’m certain he would have said ‘film’ if movies had existed at the time,” Kubrick mused. Though, when he referred to the Frenchman’s “life”, he meant it literally, his stated aim being to re-create the whole of Bonaparte’s journey from Corsican ruffian to St Helena exile, taking in the French revolution, the entire Napoleonic war and his equally tumultuous love affair with Joséphine de Beauharnais. Spanning half a century, Kubrick’s movie was to be set on a broad inter­national canvas — Lisbon to Moscow, Channel to Med. David Hemmings was his nominal “Boney”.

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