TELEVISION / An original of the species: Mark Lawson praises Molly Dineen's documentary series The Ark and appeals on behalf of an endangered species

Although established as an attraction for children, London Zoo has tended to prompt darker thoughts from adults. It is the setting for two fine dystopic novels - Angus Wilson's The Old Men at The Zoo and Russell Hoban's Turtle Diary - perhaps because apocalyptic plots offer a resonant echo of Noah, in the necessity to find a safe place for the animals.

Molly Dineen - in her splendid four-part BBC 2 documentary series The Ark, which ended last night - is the latest artist to come back from London Zoo with a metaphor for modern beastliness. Her films - in which an originally altruistic institution, losing public appeal, unsteadily attempted to make itself 'relevant' to present-day taste - made clear symbolic prods at the Labour Party, the Church of England and, not least, the BBC. Last night's climax, in which the staff engineered the removal of the zoo's bureaucratic General Director (a mere matter of word order away from the title held by John Birt), may have added a certain nervousness to the smiles of BBC chiefs at having sheltered such an excellent piece of television. The Ark is as much about animals as Animal Farm was.

The series confirmed the formidable film-making abilities suggested by her 40 Minutes documentaries: 'Home From the Hill' - a portrait of an old colonial hand's forced retreat from Kenya to a forbidding Eighties England - and 'The Heart of the Angel', in which the director's keen ear-to-the-ground extended below it in a portrait of the everyday operation of a Northern Line tube station. A good documentary is half location and half inspiration and this director has the talent of access. The result of two years' admission to London Zoo, The Ark finds Dineen on the same track as her Underground film, her signature skills growing from distinctiveness to distinction.

The first of these is that Dineen, like all top handlers of a camera, has a tone of her own. The prevailing mood of BBC documentary in the last decade - in the work, particularly, of Paul Watson, Roger Mills and Roger Graef - has been the cool view, the camera as unacknowledged watcher, any extra-visual facts provided by sombre white-on-black captions. If verbal narration was used, it was spoken by an actor with frosty authority. This style did not imply neutrality: a series such as Graef's Police or Watson's The Fishing Party, in which he caught a shoal of Eighties Hoorays, clearly communicated moral anger to the viewers. But the relationship of the camera to the material was one of chilly distance. It stalked the room like an invigilator at an exam. This was the style that became known as fly-on-the-wall. The tag had an additional neatness, because flies are attracted to dirt, and so were these films.

As in Dineen's earlier work, The Ark departs from the austere traditions of the form. Her overall approach might best be called a warm focus, although it is not a soft one. Part of the originality of 'Home From the Hill' was its anti-historical sympathy for its subject, Colonel Hilary Hook, who might easily have been presented as a sub-Wodehouse fogy. The colonel was allowed to touch the viewer.

Attempting narrative through character on a grander scale, The Ark shows the same talent for the rounded portrait and, crucially, across the social strata. As a director, Dineen clearly has either a seductive eye or a chameleon ear, by which I mean that interviewees must develop a burning urge to confide in her, or they come to forget that everything they do is being monitored. Whatever the explanation, they speak with the easy confidence of the Prince of Wales making a dirty phone call. The series is really about the human menagerie, the political and emotional species of these strange days.

My favourites were the sloth and the slug. The former was Dave Robinson, a keeper in the Tropical Birds house, a big, moustachioed, soft-voiced man, like a gloomier Graham Gooch. In the most distinctive scene in the series Dave, a Christian, required to work Sunday, skinned and sliced rodents for a mouse muesli for his birds while listening to Morning Service. 'The falcons, they like 'em skinned, ' he muttered. A dramatist would have killed to have written the scene, but they would have spoiled it by calling the radio play All Creatures Great And Small and anyway, no one would have believed it. In a good documentary the neatnesses have the defence of realism.

Dave's kind, however, were seen as sloths by the management slugs, sent into the zoo from the leisure industry as a government condition of the last chunk of subsidy. At the other end of the scale of industrial evolution from Dave was Andrew Forbes, a man with the human manner of a statue and the vocabulary of an abacus. It is rumoured that the BBC staff working on the series thought he reminded them of someone. Dineen's achievement was to make this management clam open up. When Forbes spoke of the standards he expected from his staff, the director asked whether he treated his children the same way. That she had the presence of mind to ask the question is to Dineen's credit; that Forbes had developed the absence of caution to answer it is even more so. He proudly explained that his young daughter had sold pine-cones to passers-by for pocket money. 'She will grow up a leader,' he purred.

So Dineen made it fairly clear that not all the bullshit around London Zoo had emerged from the animals. But the power of The Ark was that it offered no simple political pieties. Some sequences - like last night's in which a moist-eyed keeper nursed a koala bear with diarrhoea - made a point about love and craft not showing up on balance sheets. Yet the mere fact of the setting - a zoo, confining wildlife in an urban jungle - worked against easy liberal sympathy for the staff against the bosses. If the series was a political animal, it was a pushmipullyu: an explanation of a zoo's role in breeding endangered species dragged the viewer in one direction, film of Cilla Black reading a poem at a photo-opportunity for the arrival of a giant panda hauled you in another. Dineen's one miscalculation was in the final scene, when an eloquently bleak sweep of the abandoned bear terraces was overloaded by a keeper saying: 'Funny old country, England . . .' The point had already emerged more obliquely as, for example, when the Keeper of Mammals remarked that his staff had 'all been terribly British' about being sacked.

But, in the funny new country Britain is, Dineen's series is also a metaphor for itself. A project like The Ark needs so much money spent on nourishment, so much care and grooming in the 24-month gestation period before it is ready for viewing, that it can be bred and can flourish only within the cage of subsidised, non-commercial television. Beyond these confines, the films exhibited will need to be especially cuddly or unusually disgusting: pandas or rhinoceroses, meaning, in this context, tug-of-love babies or serial killers. But the keepers of the national free-market theme park are currently rattling the gates of the BBC's cage. Molly Dineen, and admirers of her exceptional talent, will have to hope that the management of the beleaguered national institution that employed her proves more adept at balancing tradition and new political conditions than that of the one she has so memorably captured on film. One of the things I learned from The Ark is that the panda is scientifically termed 'crepuscular', a twilight animal. We shall have to hope that Dineen's species of documentary can never be similarly described.