A long unseen Holocaust documentary, on which Alfred Hitchcock had an advisory role, is being restored with the support of filmmaker Stephen Frears.

The film will be shown in early 2015 to mark the 70th anniversary of the “liberation” of Europe.

An accompanying feature length documentary, Night Will Fall, telling the extraordinary story behind the making and suppression of the film, is being prepared by London-based production company Spring Films in association with Angel TV and The Imperial War Museum.

Details of the two projects were revealed at International Documentary Festival Amsterdam (IDFA) by sales agent Cinephil.

The film, made in 1945 by the British Army, chronicles the liberation of Bergen-Belsen and its aftermath.

Produced by Sidney Bernstein and edited by Stewart McAllister (famous for his work with Humphrey Jennings), the doc’s aim was to make it impossible for Germans to deny that the atrocities in the camps took place.

Hitchcock’s role was in advising how the material from the camps should be drawn together.

The doc features gruesome imagery of Belsen-Bergen and of other camps but was never completed. The British Government and the US State Department are reported to have stopped the film on the grounds that it would have been damaging to the post-war reconstruction of Germany.

André Singer, executive producer of The Act Of Killing, is directing Night Will Fall with Stephen Frears as directorial advisor, Sally Angel as producer and Richard Melman as exec producer.

A researcher first found the original footage in the Imperial War Museum in London in the 1980s. In 1985, this was shown in a botched and incomplete version on PBS in the US under the title Memory Of The Camps with voice-over narration read by actor Trevor Howard.

The film has now been scanned, restored and put in the correct order by Dr Toby Haggith of the Imperial War Museum. The new version includes the sixth and final reel.

“This film discusses a period that is normally not discussed,” said Philippa Kowarsky, managing director of Cinephil Distribution & Co Productions.

“[UK broadcaster] Channel 4 wants to show the two – the Hitchcock film and this film (Night Will Fall) in 2015.”

She said the project had the support of Channel 4, the BFI, ARTE, NDR, Israeli Television and the Israeli Film Fund. Negotiations are underway with public TV in the States.

“The goal is that, in 2015, it goes to all TV. In the meantime, it has a year to go to festivals and cinemas,” added Kowarsky.