This review contains some major spoilers, so proceed with caution if you are new to the film.

The story of what happened witb the TV version of Scum is well known in the British film and TV industry. Written by Roy Minton and directed by Alan Clarke, the project had been green-lit as part of the prestigious Play for Today series by BBC1 controller Brian Cowgill, but following his departure and replacement with the more cautiously minded Billy Cotton, problems arose. Cuts were requested, Home Office and prison officials were called in to view it, and the decision was ultimately made that the film should not be transmitted. Despite having been already advertised, Scum was pulled from the schedules and remained a banned work for the next fourteen years. Even then it only received a single screening on rival station Channel 4, where it was introduced by Made in Britain writer David Leland (who memorably instructed us all to set our video recorders going) as part of a season of programmes paying tribute to Alan Clarke, who had died a year earlier. Despite this sizeable initial setback, Clarke and Minton refused to give up on the project, and two years later re-shot the film on 35mm for a cinema release. The resulting work became one of the most successful British films of the year, and one that to this day remains an powerful and iconic work.

Most of those coming to the original version of Scum, myself included, did so having already become familiar with the feature film remake. This brings baggage to the viewing that is unfair and unfortunate – in my case the feature version was a key film of my youth, a work that genuinely affected my attitude to cinema in general. It was also my introduction to the work of Alan Clarke. To fully appreciate the original's qualities it is important to put that aside and to cart yourself back to the 1970s and imagine just what would have happened if you had tuned in at 9.25pm one evening and been presented, completely out of the blue, with this. Had it not been banned, of course.

For the uninitiated, Scum is set in a borstal, a word that may mean little to younger viewers, the reason being that the borstal system itself was abolished by The Criminal Justice Act in 1982. Borstals were institutions in which young offenders were incarcerated under a strict regime of harsh discipline, work and education. They were intended to teach their inmates respect for authority, install in them a strong work ethic and build character. By the 1970s, however, it was becoming clear that in a number of borstals control was being maintained by a regime of violence, bullying and racism being dished out by staff and inmates alike. Into just such an institution arrive three new unfortunates: tough, street-wise Carlin has been transferred from another borstal after hitting a warder; quiet, introverted Davis ran away from a minimum security establishment; while black newcomer Angel is unprepared for the racism he is to be subjected to by his white custodians and fellow prisoners. Carlin in particular becomes an immediate focus for attention, his reputation as a 'daddy' – an inmate in an unofficial position of power attained and maintained through a combination of violence and gangland-style intimidation – having arrived ahead of him, which brings him into immediate conflict with the warders and the incumbent daddy, Pongo Banks.

The original version of Scum is both more low key and, in some ways, more hesitant than its later feature film brother. Most of the performances lack the striking confidence they have in the film and there are none of the compellingly executed 'walking shots' that were to become a trademark aspect of the director's visual style. But this approach can also be seen as less sensationalist than the film version, and creates an intimacy with the characters that is immediately engaging and has a matter-of-fact quality that in some ways enhances its potent air of realism.

The narrative and dialogue are virtually identical to the feature, if lacking the expletives that are now seen as key components of some of the film's most memorable lines. Individual scenes sometimes unfold differently here, and there are some locational shifts, but those familiar with the feature will still feel at home. Where the two do part company a little is in the second half – in this version Carlin plays an increasingly minor narrative role, and in a compelling scene that did not make it into the film (due to Ray Winstone being uncomfortable with it, a decision he later regretted) he takes on a 'missus', a young inmate he keeps around for company and sexual gratification. This leads to a scene also unique to this version in which the increasingly despairing Davis goes to Carlin for advice, only to be dismissed out of hand when he feels unable to talk in front of this now ever-present companion. This paints Carlin in a more callous light, making his own attitude a contributory factor in Davis's eventual suicide and suggesting a stronger motivation for him to lead the riot that follows, springing as it does from his anger at himself for allowing this to happen.

As Carlin, Ray Winstone was making his acting debut here, and though he lacks the forceful authority he displays in the remake, his obvious youth and naturalistic delivery really sell the authenticity of his character and situation. This also applies to many of the supporting roles, whose increased confidence in the feature resulted in part from being able to have a second shot at characters with which they were by then familiar, a chance almost every actor must have wanted at one time or another. The character that differs most noticeably in two films is without doubt Archer, the cynical intellectual that Carlin befriends and the mouthpiece for Roy Minton's own views on the situation. Played to scene-stealing perfection by Mick Ford in the remake, the interpretation here by David Threlfall is less animated and lacking the cocky world-weariness that Ford made central to his interpretation. Threlfall, however, is just as fascinating in his own way and certainly is less of a sore thumb standout in this particular institution than his successor (Threlfall was to really prove his worth five years later with his heart-breaking performance as Smike in the Royal Shakespeare Company's production of Nicholas Nickleby).

Initially it's Carlin who drives the narrative, the beatings and humiliation he endures leading to the inevitable but still hugely cathartic scene in which he takes out Pongo and establishes himself as the new power on the block. His position is consolidated when he defeats the intimidating black boss of B wing by swinging a weapon in a fight his opponent was under the impression would be settled with fists. It's in this scene, as in the earlier one in which Angel is beaten by Pongo and then given a nasty dressing-down by a warder, that the true nature of the racist insults spouted many of the white characters is most clearly illustrated – far from being an expression of genuine racial hatred, it is used as yet another method of control, a bullying put-down employed to belittle and humiliate. That it is so direct will no doubt cause some newcomers to the story to balk a little at these scenes, but it never feels gratuitous, even at its most unpleasant.

As the film builds, simmers and finally explodes, the viewer is left with the inescapable sense of a system that does not strengthen character nor install respect for authority, but which brutalises and destroys, takes young men who have broken the rules and moulds them into hardened criminals. If the TV original never quite displays the electrifying power of the feature version, then this is only right – the demands and expectations of a cinema feature are different to that of a TV play, and it's a sign of the screenplay's strength that no significant changes had to be made to story, character or (toughening up aside) dialogue to reshape the film for cinema release. As a work of its time, a TV play made for screening on a mainstream TV channel, Scum is an astonishing achievement. That it was banned and buried by the people who should have been celebrating this is scandalous, but that there is nothing being produced by any UK TV channel now that comes even halfway close to matching the film's boldness, ambition and commitment, is ultimately depressing.

Framed in it's original TV ratio of 1.33:1, the film was shot on location for UK TV in the 1970s on high speed 16mm stock. The resulting grain is very noticeable throughout and sharpness is occasionally a tad weak as a result, but elsewhere reasonably crisp detail shines through the grain, and given the limitations of the print Blue Underground have done a most reasonable job on the transfer. Contrast is a little high in places, but black levels are solid, and it's frankly hard to see how the picture could have been significantly improved. It's certainly several steps up from my VHS tape print.

The soundtrack is 2-channel mono, and given the age of the film and the inerrant problems of filming in on location – sometimes in wide shots where microphones needed to be hidden to be effective – the quality and clarity of the sound is impressive throughout. The film's sound recordist Michael Turner really earned his money here.

Just making this rarely seen but hugely important slice of British TV history available on DVD would have been enough for me, but Blue Underground have excelled themselves through the inclusion of a commentary track featuring producer Margaret Matheson and actors David Threlfall and Phil Daniels, the discussion being hosted by critic and broadcaster Nigel Floyd, making it an all-English affair. The first ten minutes consist of a general discussion on how the project came into being, but the comments eventually become screen-specific, with background detail supplied on individual scenes and characters, and plenty of interesting anecdotes thrown in about the production itself. David Threlfall in particular appears to be having a good time. Later on, Matheson gives some very detailed information on the banning of the film, and all of the participants seem united in their admiration of Clarke as a director and colleague. Consistently engrossing and with no dead spots, this is a very fine, very useful special feature.

A second commentary track features star Ray Winstone commenting on two short scenes, Carlin's arrival at the borstal and the scene – not in the feature version – in which he takes on a 'missus'. Winstone's comments here are useful, especially his explanation over why the scene failed to appear in the later version, though his voice does sound as if it has been slowed down slightly, giving it an unnaturally deep ring. The lack of a full commentary by Winstone is not an issue, given his track on the cinema version.

As a stand-alone release this would have been exciting enough, but as part of the Clarke box set it is a dream come true. The transfer is as good as could be expected and the commentary track is first rate. The inclusion of this original BBC version of Scum in The Alan Clarke Collection, together with the equally rare Elephant, makes it more than just an essential purchase for anyone who really cares about Outsider Cinema – it marks it as probably the most important box set be released this year, and possibly the most electrifying collection of British film and television material available on DVD.

* Quoted in Alan Clarke, edited by Richard Kelly, first edition, Faber and Faber 1998