So what has changed in 30 years to make 'Straw Dogs' acceptable home entertainment?

The most shocking rape scenes in mainstream cinema history have been passed by the censor.

Thirty years after its first cinema release, Sam Peckinpah's Straw Dogs, the last of the great "banned films" of the 1970s, can finally be viewed in the comfort of your own living room. The British Board of Film Classification has agreed that the movie, which includes some of the most violent rape scenes ever seen on celluloid, can be released uncut on video.

One by one, key titles from film history's "most notorious" list have fallen like ninepins as the BBFC has relented on previous draconian decisions. Significant big name scandal movies have been passed uncut, including The Exorcist and another 1971 cinema release, A Clockwork Orange. The decisions seem even more surprising when lower budget "video nasties" such as New York Ripper or I Spit on Your Grave have paid the price of censorship in order to reach your local videostore.

But Straw Dogs? With not one, but two, disturbing, graphic rape scenes? Why should the board decree that we be allowed to see it now?

The film, with its influences from both art-house and exploitation cinema, was a big-star production and played out rather like The Wicker Man meets Pacific Heights in Hardy's Wessex. It fiercely scrutinises the redeeming power of male violence (although whether as exploration or glorification is a matter of debate).

The plot is lean: American mathematics professor David (Dustin Hoffman) brings his British wife Amy (Susan George) to Cornwall so that he can write in peace. (Here Peckinpah's Wild West is west of Plymouth, Devon, not Plymouth Rock.) Peace is the last thing he gets. If David is the stranger in a strange land, Amy is the returning native, an unsettling image of untrustworthy femininity; not quite foreign, nor quite at home. Their house is renovated by a group of feckless yokels, one of which (Charlie) is the flirtatious Amy's ex-lover. Conflict between the rich incomers and resentful locals escalates to the point of rape, and the house is besieged. David snaps, metamorphosing from mouse to man as he takes up arms.

There is no doubt that Straw Dogs was, and is, a violent film. Stephen Murphy, BBFC secretary in 1971, saw a pre-release version and advised Peckinpah to make cuts to the rape before submitting it for certification. The resulting work is still often erroneously referred to as the "complete" original version, though Murphy ensured it was no such thing. On release, Straw Dogs garnered hostile reviews, and 13 leading critics wrote a letter of condemnation to The Times. But even then British audiences were more tolerant than British critics, making Straw Dogs a considerable box-office hit.

Viewers today may find it tamer than previous generations did. The conclusive battle is uncompromising, but not unprecedented; no bloodier, perhaps, than mainstream hits such as Fight Club. But it is not just a violent film. The end-game is one thing: boiling oil, man traps, point-blank fire; by now we've seen 'em all. Amy's rape is quite another. Though gore-free, it spins the more dangerous story that women don't know what's good for them, and that "no" means "yes".

First her ex-lover Charlie drags Amy to the sofa by her hair, slapping her around a bit on the way, and then he rapes her. If this weren't bad enough, repulsion turns to seduction, with Amy's body warming to the point of orgasm, her ecstatic expressions and grateful tears shot from the rapist's point of view. Then as Amy lies face-down in a post-coital stupor, she is penetrated by a second man, which she bitterly resists. (The fact that in the "Murphy version" this rape looks like sodomy, whereas in Peckinpah's version it allegedly looked like vaginal rape, only complicated the situation for contemporary critics.) More shocking than the violence itself is the way in which the second rape casts a beam of approval across the first: Straw Dogs distinguishes between "good" rape (the first) and "bad" rape (the second), how you respond depending on who the rapist is.

This makes the BBFC's recent justification for its decision to pass it on video all the more surprising. In 1999 a cut American version was submitted for certification, containing a shorter version of the second (unpleasurable) rape. The BBFC rejected the film because "the issue of sexual violence has become of greater concern for the board than 20 or 30 years ago". They objected to "the clear indication that Amy comes to enjoy being raped"; with less of the second rape present, the first loomed larger. At that time the BBFC actually suggested further cuts, which the distributor declined.

In 2002 the board was shown "substantially the original uncut version" which contained a fuller version of this second rape (the Murphy version, in fact). The BBFC is arguing that: "The ambiguity of the first rape is given context by the second rape, which now makes it quite clear that sexual assault is not something that Amy ultimately welcomes." In essence, the more of the second rape we see, the less palatable rape becomes, even though the first "enjoyable" rape remains intact.

But how exactly does more of the spectacle of Amy's suffering in the second rape alter the fact that she liked the first one? In Straw Dogs, how you respond to rape depends on who is doing it to you; for the BBFC the more of the second rape we see, and the more of Amy's suffering we witness, the less we are likely to remember about the time she enjoyed it.

The question for the board remained, was it titillating? Key to the BBFC's decision is the advice it took from clinical psychologists. The board asked three of them – all doctors who were dealing with sex offenders – to view the tape individually. Sue Clark, spokeswoman for the board, said: "More and more we're taking advice from clinical psychologists particularly on the issue of imitation." The psychologists' response was that "the present version of Straw Dogs was not harmful and was not likely to encourage an interest in rape or abusive behaviour to women".

Clinical psychologists were also used by the BBFC to view two recent documentaries on sado-masochism, Didn't Do it for Love and Sick – the Life and Death of Bob Flanagan, Super Masochist. These said Clark, "included explicit footage of self-mutilation with no on-screen warning. The scenes depicted activities which could be lethal if someone attempted it themselves." The psychologists were asked what they thought would happen if people vulnerable to this kind of sexual practice watched them and in these two cases imitation was considered likely. So those scenes were ordered to be cut.

The difficulty with the board's decision on Straw Dogs is that it shows the BBFC to be inconsistent in its approach to cinematic rape. I Spit on Your Grave lost a mighty seven minutes and two seconds from a gruelling gang rape, and the censors are currently demanding multiple cuts to Wes Craven's Last House on the Left for video certification. Straw Dogs needed more sexual violence to make it acceptable; these other films needed less. Yet it is only Peckinpah's film which ever flirts with the idea that rape can be pleasurable for the victim. Even that venerable libertarian George Melly, who reviewed Straw Dogs on its first release, was shocked enough to note: "Sex and violence are constantly equated in this film. The gun and the cock are interchangeable."

Whether this will be as significant a problem to home viewers in 2002 as it was for cinema critics in 1971 remains to be seen.

Dr Linda Ruth Williams lectures in film studies at Southampton University. She is author of the forthcoming book 'The Erotic Thriller in Contemporary Cinema'