She was a real head-turner in her day but, 27 years later, her ability to surprise and shock has lessened.

Regan MacNeill's devilish behaviour of vomiting green bile, uttering foul language and doing unmentionable things with a crucifix made 1970s cinema audiences scream and faint in the aisles when The Exorcist was first shown.

Tonight, the terrestrial premiere of William Friedkin's controversial horror movie is likely to pass with little more than a few murmurs of disapproval from more sensitive viewers and religious organisations.

Back in 1973, the story of the exorcism of Regan, a 12-year-old possessed by the devil, put people in as much of a spin as the poor girl's head when it did a full 360 degree turn in one of the film's most famous scenes.

Movie audiences had never seen anything like it before and, thanks to the British Board of Film Censors (now Classification), didn't see it on video for 25 years. The film was re-released in 1998, the year before the BBFC finally removed its ban, passing it uncut with an 18 certificate for video.

The film's power to upset and alarm has diminished since the original release, partly because the primitive pre-Star Wars special effects are poor compared to today's computer-generated trickery. For instance, because Friedkin wanted to see the actor's cold breath in a scene in Regan's bedroom, the enclosed set had to be refrigerated overnight to achieve the same effect that was added afterwards by computer-generated effects in the recent Titanic.

One trick Friedkin employed, and one which worried some people, was insert subliminal images - flashes of pictures only detectable if you freeze frame the picture. Then Regan's face changes. The images used were actually pictures of rejected make-up tests for the character's possessed look.

The Exorcist remains scary but the glut of devil-worship movies that followed and countless movies featuring much more extreme violence and imagery have robbed the movie of real shock value. Viewed today, it's hard to imagine what prompted critics to call The Exorcist "a thoroughly evil film" and "an insult to the intelligence and a disgrace to the cinema".

Novelist William Peter Blatty based his supernatural tale on a real-life case of the possession and exorcism of a teenage Canadian boy in the 1940s. Several other directors were considered until Friedkin, who'd won an Oscar for The French Connection, was signed up.

Shooting the film didn't always proceed smoothly. He and Blatty argued on the set to the point where the writer tried to have him fired from the project. The director allegedly slapped a real priest in the cast to get the right reaction on camera. Several times he's alleged to have fired a gun on the set.

The Exorcist received ten Oscar nominations, including a best picture nod, but won just two, for Blatty's screenplay and sound.

The legacy of The Exorcist includes a theory that a curse has affected cast and crew. Deaths, injuries and even the slump in Friedkin's career have been blamed on its influence. Yet, the director shows no sign of abandoning the film even now. Last year, he reinstated several deleted scenes, including Regan's spider walk, for yet another cinema re-release.

* The Exorcist is showing on Channel 4 tonight at 10.30p