THE form may have been diminished by endless parodies, but there is still something thrilling about a traditional investigative documentary. The thrill of the chase, the late-night stake-outs, and the final confrontation - it is what journalists used to do.

Stories in Sound (Radio Ulster, Thursday of last week) felt like a blast from the past. We heard the Northern Ireland reporter Andy Pag on the trail of people-traffickers, in a piece that combined revelation with a critique of the forthcoming law in Northern Ireland to criminalise payment for sex. The title, Vice Girl or Victim?, set out the issue: although many young women could technically be said to enter into the sex trade by consent, there is, with most, a high level of coercion arising from financial circumstances.

Pag's investigation focused on the influx of Chinese women into Belfast, answering ads for masseurs - and, for the most part, knowing what extra services "massage" entailed. In a simple but effective sting, he confronted a ringleader, and, microphone in hand, chased her down the street, bombarding her with embarrassing questions.

This sort of thing will always be great radio, but the wider question - whether the new legislation will make debt-ridden migrant workers more desperate - remained hanging. With an economic downturn in China, it is hard to see how the destinies of women such as "Fay", or "Lynn", featured here, are going to improve.

An émigré story in a somewhat less depressing vein was that of Arthur Orton - or, as he would have it, Sir Roger Tichborne. Friday's edition of The Essay (Radio 3, weekdays) recounted how Orton, a Wapping butcher who had emigrated to Wagga Wagga, Australia, almost succeeded in claiming the Tichborne family inheritance.

Orton's campaign of deceit began with what might seem the most unpromising of strategies: he sent a photograph of himself to Lady Tichborne, the elderly widow who had initiated a search for her estranged son.

Remarkably, she welcomed her "long-lost son" with open arms; and thus began one of the longest and most expensive cases in British legal history, lasting from 1867 to 1874. For the Radio 3 essayist Jennifer Tucker, the interest lay in the status of the photograph as witness to the truth. These were the early days of photography, before we routinely questioned the veracity of the images.

It also raised discussion about whether a man's physical appearance and moral character might change, in keeping with diminished and degrading circumstances. The case of "The Tichborne Claimant" became a case-study in the nature-versus-nurture debate.

A parallel case-study of breeding and environment might be conducted at the Hollywood Cricket Club, where the manners and gentility of the great English game are practised amid the dazzle of the film industry. In Sports Hour (World Service, Saturday), we heard about this eccentric partnership of English mores and LA glitz, initiated in the 1930s by the English actor C. Aubrey Smith, and continued by the likes of Hugh Grant and Mick Jagger. Even the grass seed in the playing area is imported from Blighty.