“Something happened in here... something beyond our understanding at the moment...”

Hammer's first official foray into the world of horror starts very promisingly, as something flies low overhead and crashes, causing panic and mayhem in the British countryside. Unfortunately, that somethingturns out to be a comically up-ended rocket-shaped rocket (like in the Tin Tin books), nose in the ground and otherwise unharmed. Just like real life, then.

First the Trumpton fire brigade are called out to deal with it, assorted overcoat wearing cigarette smokers told to "keep clear". Then Professor Quatermass arrives in an old VW Camper Van. And what a git he is, not at all bothered about the three men supposedly trapped inside, but more concerned with his reputation. "I launched it - I brought it back. That's quite an achievement, I think."

They take a chance and open the door, despite the hull being so hot anyone left inside would instantly cook. One bloke in what looks like American footballer gear crawls out - but where are the other two?

The one survivor is astronaut Victor Carroon, and he's not a well boy. His only words are "help me" before he's carted off in an ambulance.

Quatermass X-periment (the title designed to take full advantage of the spanking new X certificate) must have been unlike anything the 50s audience had ever seen before. It sets out its stall within the first couple of minutes - there will be no hysterics, no mad ideas, no compromise. What you're going to see could happen (inverted rocket crashes aside) and we're going to show it to you in graphic, documentary style. It's no wonder the film caused a sensation at the time. Apart from the 50s setting, the film's hardly aged at all.

Quatermass goes off to see the police - but not to ask for advice, or warn about impending alien invasion - no, he's wanting to complain about the way the crash scene was handled. The inspector in charge (Jack Warner, prior to his Dixon Of Dock Green days) gets torn off a strip: "You might almost say we've been given a rocket," he jokes (after Quatermass has left).

As Victor's bones and skin start changing, Quatermass reveals he can't pronounce "metabolic" (Brian Donlevy was apparently completely pissed during the entire shoot - if this is true, it's hardly noticeable) and spouts stuff like: "On the other side of the air there is a whole new world out there..." and "Would a hospital know how to deal with a man who's been exposed to rocket radiation?" (You'd hope so...)

Victor's fingerprints now "aren't even human", and, as Quatermass says: "Something happened in here (the rocket)... something beyond our understanding at the moment... if only I knew where to begin..."

As they try to work out what the "jelly" they've found on the floor of the rocket could possibly be, Carroon's wife Judith freaks out, telling the Prof: "You have destroyed him, like you have destroyed everything else you have touched!"

A film taken from the rocket's CCTV camera is finally developed, and we're treated to another tour de force from the film makers. Deciding not to go with the usual (extremely annoying) method of treating the audience like idiots and showing them a professionally done film-within-a-film complete with zooms and moving cameras, the footage is grainy, shot from a fixed point, and all the more frightening for it, as the astronauts are seen silently succumbing to an unseen force.

Of course, it's not long before Victor escapes and his true alien roots are revealed - he's no longer human, but a being that can absorb other living things - plants, people and animals (he lays waste to an entire zoo at one point).

The similarities to Universal's Frankenstein series (this was years before Hammer's "official" version of Shelley's tale) are clear - the way Victor rises stiffly from his hospital bed, his pain and horror at what he has become - there's even a scene with a little girl who isn't scared of him.

"Victor" also tries to kill himself at one point, but fails (the annoying chemist gets it instead) and there's a fair amount of gruesomely deflated bodies now left in his wake.

As the monster starts to grow and sheds the last vestiges of humanity, the final showdown takes place in Westminster Abbey (before the cameras of a BBC documentary crew led by a very youthful Gordon Jackson). Unfortunately, as with the sequel Quatermass 2, it's a marvellous idea let down by the usual problems of budgetary constraints. The last thing we see is an unrepentant Quatermass walking out on everyone, muttering: "I'm gonna need some help... gonna start again..."

Despite a slight anti-climax, The Quatermass X-periment is an awesome film - still unnerving, way ahead of its time, and of course, the beginning of British Horror's golden age. For that we should be more than grateful.