As Bob Roberts kicks off and the main title passes, we are informed that we are watching 'a documentary by Terry Manchester'. Even if you come to the film with no foreknowledge of its content, you'll soon know this is nonsense. After all, as the title character takes the stage it will be an uninformed filmgoer who doesn't recognise that Roberts is actually Tim Robbins. Oh come on, he's on the poster as well.

I'm assuming that by now all film enthusiasts are familiar with the term 'mockumentary'. A typical example of modern lingual mutation, the films that sit under its umbrella generally fall into one of two categories – comedies that use the techniques of documentary to tell their story (This is Spinal Tap, Bad News Tour, Best in Show) and fake documentaries designed specifically to hoodwink the audience (Ghost Watch, Forgotten Silver). With it's name actor cast and sometimes non-documentary look, Bob Roberts definitely falls into the former camp. But despite its share of comic moments, it has more serious issues on its mind.

So who is Bob Roberts? He's a successful reactionary folk singer turned Republican politician and is on the campaign trail, a ripe subject for the fictional documentary film-maker Manchester. Initially intending the film to be both a record of the campaign and a portrait of the man, Manchester starts to uncover signs of a darker side of both Roberts and his shady campaign manager Lukas Hart III, then finds himself bearing witness what could be a dramatic turning point in American political history.

Bob Roberts is portrait of a political monster for the modern age, a right-wing crusader who trades on his entertainment background, his good looks and his squeaky-clean image, and who feeds off and encourages the shallow prejudices of his adoring admirers. He is charismatic, intelligent and charming; that he is presented as such by both Robbins the director and Robbins the actor is crucial to the film's intent and our initial engagement with Roberts as a screen character. But his politics are that of prejudicial rhetoric, constructed from tabloid headline buzz-phrases and designed specifically to play on the intolerances and self-centred greed of his enthusiastic admirers. In the manner of many media-trained politicians both here and in the US, he avoids real debate in favour of sloganeering, and if directly challenged he falls back on the charge of biased reporting without ever confronting the issue at hand.

But his most direct electioneering is done through his music. Oh, the songs! Gleefully and energetically performed folk/country crossovers, these are the film's most disturbing and effective creations. Catchy, well produced and enthusiastically sung, they denounce the unemployed, drug users, liberals and progressive schoolteachers with equal starry-eyed cheer, extolling instead the virtues of unquestioning patriotism, greed and financial investment. Their polished arrangement and upbeat tempo jars with the sometimes horrifying lyrics – "Be a clean-living man with a rope in your hand!" goes a chorus-line of 'Drugs Stink', following a cry to string even the most casual user "up from the highest tree, without a trace of sym-pa-thy!" At one point, watching Bob belt out a number to a crowd of wide-eyed admirers as they whistled along, I was reminded of the 'Tomorrow Belongs to Me' scene from Cabaret, a genuinely terrifying sequence in which the beautiful singing voice of a strikingly handsome member of the Hitler Youth rallies a small crowd into a chorus of blind, patriotic hate. Perhaps the most alarming aspect of Roberts' songs is that they are not in themselves an exaggeration of reality – stuff like this is out there and not too hard to find. Surely it's only a matter of time before the Daily Mail or the like offers the soundtrack CD free to its readers with the advice to listen carefully to these prophetic words of widsom.

Roberts is symbolic of a very real aspect of the New Right, the post-80s, greed-driven conservative with contempt for everyone with a social conscience. But he also reflects the shifting values of a significant portion of Western society, the communally-minded hippies of the 1960s and 70s who went on to become mega-wealthy businessmen in the 80s and 90s. Like many of the big corporations of today, Roberts has no ideas of his own and is just recycling and repackaging those of others, appropriating and then inverting the messages, songs and imagery of the previous generation. The specific touchstones are Woody Guthrie and particularly Bob Dylan, whose album covers and iconography Roberts apes and whose song titles he perverts – 'The Times Are Changin' Back' is a gospel-driven call for a return to unquestioning patriotic obedience of previous generations. This link is emphasised by the film's repeated structural and visual references to D.A. Pennebaker's milestone vérité documentary record of Dylan's British tour, Dont Look Back, even parodying specific scenes from that film: the misdirected backstage walk that here first exposes Roberts' dark underside; the impromptu meeting with the local mayor's wife and three devoted fans; the sequence from Pennebaker's film in which Joan Baez croons as Dylan types (Roberts, of course, is using a laptop, while singer Clarissa Flan, Roberts' musical partner-in-crime, softly warbles a tune that dismisses the efforts of all protestors as the product self-interest, a bit rich coming from the Roberts camp). There is even an astonishingly realised parody of Dont Look Back's legendary opening sequence, in which Dylan stood in an alleyway peeling off lyric cards to Subterranean Homesick Blues, horribly turned around here to encourage the audience to think only of themselves and get rich by any means possible.

The film also reflects on the shallow nature of politics of image, where the policies of a candidate are deemed less important than how he looks on TV and advertising billboards. In this respect Roberts – youthful, good-looking, smartly-dressed and with the whitest of ever-present smiles – has far more appeal than his socially minded opponent Brickley Paiste, a middle-aged man who rarely looks happy and whose clothes are functional rather than a fashion statement. This again transcends party and even national boundaries and will have resonance in the UK for anyone old enough remember Michael Foot, a committed and whip-smart Labour Party leader who was repeatedly attacked in the popular press for his unkempt hair and his scruffy dress sense. Boy, the party image makers must have been hugging themselves with glee when Tony Blair first flashed that tombstone grin...

The performances are generally on the nose, though there is a little wobbling at the edges, reflecting the film's dual concerns of political drama and satirical comedy. Robbins is note-perfect as Roberts, with his boyish grins, knowing looks at the camera and wildly enthusiastic singing only occasionally allowed to slip to reveal the furious anger that bubbles just beneath. As Roberts' right-hand man Chet MacGregor, Ray Wise is a constant delight, flashing a friendly smile whenever he realises the camera is on him and cheerfully steering the crew away from anything he believes might show Roberts in an even slightly negative light. Alan Rickman makes for a thoroughly shifty Lukas Hart III, occasionally coming across as a Doctor Strangelove-like figure who is fighting the urge to bark out allegiance to his Führer, and as Senator Brickley Paiste, Gore Vidal has the right note of weariness, even if his own lack of acting experience does intermittently show. Slightly less convincing is Giancarlo Esposito as muckraking reporter Bugs Raplin, his relentlessly twitchy determination coming across as just a little exaggerated, although in the interview following his release from jail on a framed-up charge, this very nervousness takes on the air of a man genuinely frightened for his life and for the future of his country. Perhaps the most cartoonish of all are the three young Roberts devotees who follow him on tour (one of whom is played by a young Jack Black in his first feature role), whose wide-eyed obsession with their hero is mugged up to sometimes comical extremes, but which nevertheless provides the film with one of its most chilling final images. The peppering of small roles with famous faces can either prove a distraction or add to the fun, depending on your viewpoint, but this IS satire, after all. And for cineastes there is an extra layer of enjoyment to be had from the faux-documentary technique (which includes, at one point, engaging the cameraman in a discussion, to which he contributes by nodding the camera in agreement) and the various aforementioned nods to Dylan, Guthrie and Pennebaker.

For a directorial debut, Bob Roberts is a bold and impressive achievement, an entertaining but biting and ultimately disturbing political satire on the shallow nature of image-driven politics, on the ease with which rhetoric can usurp thoughtful debate, on recentreactionary anti-1960s attitudes, and on the fragile nature of democracy itself. Robbins creates in Roberts a character that runs so close to the truth at times that some have attacked the film for suggesting that such a man could be involved in corruption and guilty of deliberate deception – they have no trouble with his politics, just the tainting of his public image with scandal. There is some comfort to be taken from the knowledge that were Terry Manchester and his documentary for real they may have the necessary material to bring Roberts down, and if Robbins' film prompts even a few to think more carefully about the words that come out of their politicians' mouths, then it too will have done its job.

At last. After years of cropped 4:3 prints, even on specialist film channels, we finally get the film in its correct aspect ratio of 1.85:1, anamorphically enhanced, and looking damned good, with sharpness, colour and contrast about right and black levels pretty solid throughout. There is a little grain evident in places, but it is neither distracting nor coarse enough to look deliberate – despite the documentary influences, there has been no attempt to give the film a low budget vérité look.

The Dolby 2.0 surround track is clear and exhibits some good separation, especially in the music numbers, which are considerably louder than the centre-set dialogue and can give you a start if you've set your amp volume by the talk rather than the music.

Not a bloody thing. This is a real tragedy, as a commentary by Robbins (check out his one for Dead Man Walking) would have been seriously welcome. I would certainly like to have known more about the recruitment of so many name faces, and in particular the decision to include what was clearly an outtake of Fred Ward as a newscaster bumbling over his words, as well as American political references that I no doubt I missed. But there you go.

Fine, fine film, decent transfer, no extras. Worth buying? Well the film alone is the sell here, and on that basis I'd have to say yes, especially at the low price it can be found for online. An opportunity to create a more featured edition has been seriously missed here, but it still comes recommended for the feature, which demonstrates just how smart and talented Mr. Robbins is, and, set against the background of an impending invasion of Iraq, is as worryingly relevant now as it ever was.