Alien was originally written by Dan O’Bannon - who co-wrote and co-starred in John Carpenter’s 1974 sci-fi comedy Dark Star. When the film failed to find an audience, O’Bannon suggested to friend Ronald Shusett that perhaps it was easier to write something that would scare people than make them laugh. Thus, they set to work on a script which would one day become Alien. The original title: “Star Beast.”

Before deciding to make Alien, Ridley Scott had been planning to follow his first film, The Duellists, with an adaptation of Tristan and Isolde. He changed his mind after being invited to a screening of Star Wars. “I thought ‘I must be out of my mind!’” he later recalled. “This is what cinema is about!” Scott soon abandoned his plans to make Tristan and Isolde and let his agent know that he was looking for a science fiction film.

When Scott received the Alien screenplay, he was immediately hooked - “right from the first page. In fact, I finished the thing in a single go, in under an hour and a half, which is an extremely rare thing for me to do. I was so impressed with the Alien screenplay that, within twenty-four hours of my reading it, I had decided that this would be my next film.”

Ripley was originally scripted to be a male character. When one of the producers suggested that they could change all the rules of science fiction films by making her - essentially the hero - a woman, Ridley Scott embraced the idea and a movie legend was born.

According to Ridley Scott, fresh oysters and clams were used for the facehugger innards. Model soldiers and children in spacesuits - including Scott’s two sons, now both directors in their own right - were used to portray miniature astronauts.

Actress Veronica Cartwright, who plays the part of Lambert, was originally cast in the role of Ripley. She only found out that she was playing Lambert instead when she read the nametag on her uniform during costume fitting. “I thought I was playing Ripley,” she says. “That’s the only part I’d ever read for, so that’s what I thought. I’d never even looked at the script from the point of view of Lambert, so I had to re-read the script.”

The ‘chestburster’ scene, arguably the film’s most famous, was achieved by having John Hurt sit in a deckchair under a table, with his head joined to a false body, leaving his head writhing and his arms thrashing. (A similar technique is used when Ash’s severed head is revived later in the film.) Scott had not warned the cast what would happen when the creature burst from John Hurt’s chest - that they would all be sprayed with pig’s blood - because he wanted their reactions to be real. They are.

The ship at the centre of the story was originally named the Snark, after the legendary creature being sought in Lewis Carroll’s poem The Hunting of the Snark. Its next name was Leviathan - a reference to its enormous size - before Scott eventually settled on Nostromo, the title of a novel by Joseph Conrad, a quotation from whom opens the screenplay: “We live as we dream - alone.”

In addition to being restored and remastered, Alien: The Director’s Cut incorporates several minutes of footage never before seen in cinemas: notably a scene in which Ripley (Sigourney Weaver) discovers Dallas (Tom Skerritt) cocooned by the alien creatures.

Released on 25 May 1979 on just 91 screens - far fewer than the release of Alien: The Director’s Cut - Alien grossed just $3.5 million during its weekend debut, but went on to earn a massive $78.9 million in the US alone.