IN 2010 the British Film Institute (BFI) set up an initiative to track down 75 of the most important British films to have gone missing since they were first screened. "Missing" is a relative term as some of the titles on the list are in fact available on DVD. What the BFI is searching for are prints or negatives, something as close to the original material as possible.

The list contains early silent movies from the 1910s and 1920s, but also some that are surprisingly modern: five films from the 1960s and several from the 1970s, including “Symptoms”, a cult horror movie. Among the most celebrated on the list are “A Study in Scarlet” (pictured), shot 100 years ago and Sherlock Holmes’s first appearance on celluloid, and "The Mountain Eagle" (1926), Alfred Hitchcock's second outing as a director.

The Economist spoke to Brian Robinson, who has worked at the BFI for over 25 years and is an expert on its archive, about how films go astray and how, sometimes, they get found again.

How do the films go missing in the first place?

Well, there’s no law of copyright on film. If you make a movie, you shoot it, the negative is processed, it becomes a film—35mm, 16mm—it’s copied, distributed by a commercial distributor and seen in cinemas for a relatively short time. After that, it will sit on a shelf. Even if you are Orson Welles and you make a film, it’s well reviewed and shown in cinemas, if the film company that owns the negative and the distribution prints goes bust then, well, it costs money to keep things on shelves.

There are thousands upon thousands of films in archives, and archives often have little money. In the confusion of so many reels of film, things are mislabelled or lose their labels. Lots and lots of films were destroyed or lost; some were burned for their silver content; other elements in them were used to make things like Bakelite. Nitrate film is a highly combustible, unstable medium—it starts to decay as soon as it’s made.

The notion of retrospectives and film being an art form to be appreciated was an idea that was quite long in coming. Film was seen as disposable: as pure entertainment that flickered for its moment on the screen and then disappeared.

How have film prints and negatives survived at all?

Some people—slightly obsessive collectors—believed in the power of film right away and so haunted the bins of film distributors, and their collections have ended up with us. Sometimes people have left premises and hidden films under floorboards, or in attics, hen houses, churches and universities. Think of a space: there’s probably been a film found it in somewhere along the line. Kodak thought that a nitrate print would have a 50-year lifespan but we’re still discovering nitrate prints to this day that by strangely fortuitous circumstances have been kept at the right temperatures, haven’t been damp or handled by people with sticky fingers. Some of them survive in fantastic condition, and even if there’s buckling or colour fading (although most aren’t colour), with digital technology with something that to the lay person would look impossible to project from we can get extraordinary results.

What are the criteria behind the 75 films on the "Most Wanted" list?

We look through our holdings and identify key cultural and artistic gaps. Early works by well-known directors, first appearances by individuals, films which were famously well reviewed but have disappeared. There are very few art forms where as much as 80% of the output before 1929 no longer exists.

What was it about “A Study in Scarlet” that made it special enough to be included on the list?

Well, it’s based on a Conan Doyle novel and it’s the first feature that included Sherlock Holmes. Sherlock Holmes knew an immense popularity in Victorian England and actually it’s never really been unpopular.

Are the 75 films ranked in order of importance?

No, they’re ranked in date order. But in terms of importance it’s probably Hitchcock’s “The Mountain Eagle” from 1926. The most recent one on the list is “Where is Parsifal?”, which was screened in Cannes in 1983 and then never seen again. It starred Tony Curtis, Donald Pleasance, Erik Estrada and Orson Welles, with Terence Young as the executive producer.

Is there still hope of finding them?

We have found some of them. Fifty years ago if you told people that the original version of “Metropolis” would turn up in a Buenos Aires film society they might not have thought it probable or possible, but it happened a couple of years ago. And the Mitchell & Kenyon Collection: 28 hours of one- to two-minute films were found in really excellent condition—really tightly wound in three metal bins—in the basement of a shop in Blackburn about 20 years ago. With that one find our holdings of film from before 1910 went up by, I think, a third. A film that Hitchcock worked on was found in a New Zealand archive recently. We’re hoping that more will come out of the woodwork.