This excellent, albeit notorious, film has been regularly available in cinemas since its controversial debut in 1974, when it was given the old "X" rating. But only last week - 25 years later - did the British Board of Film Classification (of which I became president in January 1998, and thus an "authority") classify it for the video market.
Cinemas are well regulated in terms of observing the age categories. While there can be some slippage in films classified at "12" or even at "15" because children do not always look their age, it can be assumed that the "18" category is reliably policed. In other words, the "18" rating in the cinema means "adults only". Indeed I would say "informed adults only" for people must always have some idea of what kind of movie they have come out to see. In fact, the board has not refused an "18" classification for a film in the cinema for eight years, but occasionally it has insisted on brief cuts.
When videos enter the home, however, one cannot assume that the age classification will be observed. Even where parents conscientiously regulate their children's viewing, they cannot control what their young ones may see at their friends'. Like television, where viewers often have no idea what to expect as they move from one channel to another, videos can be carelessly picked up and played. Both television and videos can have the quality of being unbidden.
On the other hand, the board does not assume that every 12-year-old, for instance, will wish to watch every "18" video that his or her parents may rent. That depends much more upon the subject matter, the style and the actors.
In the case of The Exorcist, which we classified at "18", the board made two assumptions: that so famous is the title, most kids would want to see it; and that many parents are aware of the film's reputation and that they would take such precautions as they might think to be appropriate.
There is also an enormous difference between the economics of the two markets, and this has an impact on the way they are regulated. Films made for the cinema, rather than directly for the video market, are expensive to produce and to promote, and the board receives about 400 a year for classification. The bulk of them have wide appeal.
But the board is sent about 4,000 videos each year. Only about a tenth of these will have been in the cinema; the rest are cheaply produced, solely for video rental and often serve niche markets. If the cinema is still a bit like the theatre, the video market resembles book publishing with a similar ability to satisfy small interest groups.
The majority of these are unexceptional. But among the interest groups, one is pretty big - the buyers of so-called "adult" or pornographic movies, in turn dividing into heterosexual or gay, and subdividing again into specific sexual activities. Alongside explicit sex, there is also a niche market which relishes violence on screen, and, of course, often sex and violence are combined.
These two aspects of the video market - the fact that videos come into the home and that some will be more sexually explicit or more violent than is generally so in the cinema - explain why the legislation governing the classification of videos is much stricter and more precise.
As far as the cinema goes, the board carries out its work on behalf of local authorities, which are able to insist that local cinemas observe the board's classification decisions. Our legal duties are limited to making sure that works are not classified that would breach the Obscene Publication Acts, or which would infringe the Protection of Children Act (that makes it a crime to produce or publish indecent photographs of a child), or which would break the pre-war law which forbids any scene where animals were treated cruelly in the making of it.
Recently, too, the European Convention on Human Rights has been made part of English law and with it, Article 10, which guarantees the right to freedom of expression.
While all this legislation applies equally to videos, there is an extra consideration - the Video Recordings Act. This has been amended twice since it was first placed on the Statute Book in 1984. Some members of both Houses of Parliament continue to wonder whether it is sufficiently effective.
At its centre is the notion of "harm" - harm to those likely to view the video and harm to society through the behaviour of those viewers afterwards. And it singles out five activities as being potentially harmful - criminal behaviour, the use of illegal drugs; violent behaviour or incidents; horrific behaviour or incidents, and human sexual activity.
The Exorcist contains scenes of violence and sex, but it is not these which prevented video classification for so long. The film, with its treatment of demonic possession, was found so frightening when it was first shown that some young women fainted. That has been the problem.
On the other hand, to be terrified by a piece of fiction, whether a book, a play, a television production or a film is not necessarily to be harmed. After all, many people in their leisure activities seek briefly to feel alarmed; they pay good money for frightening experiences whether at the fun fair, or on the mountains in winter, or at the cinema.
The question which has taken so long to answer is whether The Exorcist's undoubted power to induce fear can be harmful in the sense of permanent psychological damage.
You can say that this is an unanswerable problem, and I confess that many of the issues which the board faces feel like that, but, nonetheless, have to be resolved. In this example, unusually, we had something to go on. It is this. In 25 years, no cases of psychological damage arising out of viewing The Exorcist have come to light. It was available on video, uncut, in the United Kingdom until the passing of the Video Recordings Act in 1984.
It has been in video shops uncut in Europe for many years without any adverse reaction being recorded. The film was again shown in British cinemas last autumn; there was no hysteria. How do we know there has been no incidence of harm? Of course we cannot be certain; but lobby groups would have rushed to inform us if there were examples. Still, waiting 25 years was a bit excessive - even for the authorities.