Whereas the policeman on Tristan da Cunha dutifully mans what must be the world's least productive speed trap, and dreams of the day when he may be able to use his quick-application handcuffs (a present from the British force which trained him) - policemen on the Castlefield estate probably get through several pairs of handcuffs

a year

If you're thirsting for community spirit, Tristan da Cunha offers it at 100 per cent proof - distilled, as an ex-islander appealingly put it, "by the experience of limited resources, fatal accidents and famine". A lump of volcanic rock, isolated in the middle of the South Atlantic and home to around 300 people, this is a place where everyone knows everyone else and no one has to endure troubles alone. Crime is almost unheard- of because there's nowhere to run to and not a great deal to steal in the first place.

Castlefield Estate in High Wycombe, on the other hand, is a place where the community spirit long ago evaporated, leaving nothing but an unsightly stain on the local crime records. Whereas the policeman on Tristan da Cunha is a figure of comic pathos - dutifully manning what must be the world's least productive speed trap and dreaming of the day when he may be able to use his quick-application handcuffs (a present from the British force which trained him) - the policemen on Castlefield estate probably get through several pairs of handcuffs a year, such is the criminal vigour of some of its residents. As a study in contrasts, Under the Sun's portrait of obligatory communitarianism (BBC2) and The Force's report on a new approach to policing sink estates could hardly have been bettered.

Uwe Kersken's film about Tristan was essentially a home movie, a portrait of the island narrated with an engaging amateurism by Elaine Repetto, who left to work as a nurse in Glasgow and was returning here to show her parents their grandson. She was insistently proud of its communal virtues - and slightly defensive of its peculiarities. "Women have other things to talk about," she said after the camera showed segregated groups celebrating the annual supply delivery, "so why not sit separately?" When she pointed out the holiday cottages built amid the cherished potato patches - a mere two-and-a-half miles from town - there was a trace of acquired astonishment mingled with affection. But an appreciation of Tristan da Cunha's qualities seems to come more easily to those who aren't forced to enjoy them for 365 days a year. Many younger islanders - particularly women - fantasised about leaving for places that offered the liberation of urban anonymity, the relief of nobody caring.

They would have found it on Castlefield estate, though in doses that might well have proved fatal. Mutual mistrust and a horrendous burglary rate had resulted in a community fortified against itself - many of the houses being surrounded with razor wire, security cameras and steel shuttering. There was a black comedy to some of the details here: the local neighbourhood watch (a scheme whose only weapon is publicity) is forced to operate as a secret society, because anyone known to be involved is immediately targeted by vandals. When the police put up "Burglar Beware" notices as part of a new initiative to raise their own visibility on the estate, all but one of the signs were stolen within two hours.

David Rose's report followed the progress of Operation Cruiser, an attempt to change the methods of policing from sledgehammer raids at dawn to a kind of blue serge social work - tackling the hostility and suspicion that made it difficult for law-abiding residents to resist the intimidation of the really dogged criminals. The headline buzz-words were "working with the community", a mission statement that obviously hadn't been fully digested by those involved, since several pillars of the community learned they were to be worked with only when the television cameras turned up to film the process. Nor were the results of the experiment conclusive - after five months burglaries were down by 30 per cent, but was that because a dim light of civic responsibility was beginning to dawn on some of the burglars, or simply because the place was, for the moment at least, crawling with beat policemen? With the memories of Tristan da Cunha fresh in your mind you couldn't help but feel that transportation might be a better solution for the truly incorrigible - a Force 10 Atlantic storm delivering a more persuasive argument for the virtues of mutual respect and co-operation than any amount of hearts-and-minds chat from a smiling bobby.