IT'S DIFFICULT, unpopular time-consuming and expensive. So why does anyone do it? Beyond a few pockets of radio and television, there is a reluctance nowadays to commit resources to the sort of journalism that tackles miscarriages of justice or campaigns to change laws.
But the successes, when they come, demonstrate the best of what journalism can achieve: a contribution to the health of a democracy, First Tuesday's campaign leading to the release of the Guildford Four is the most compelling recent example and represents a significant achievement.
Investigative television's strength is in making a human, emotional and immediate. It regularly draws audiences of double the combined circulation of broadsheet newspapers, an audience made up of many constituences of opinion. It has the ability to make injustices common property.
Paul Woolwich, newly appointed editor of Thames Television's This Week, argues that investive journalism almost always works. "If a programme changes even one person's view of what's being done in their name, then it's a success."
Much more difficult to achieve are legal or procedural changes. Television can engage an audience through personal accounts, but problems can get dangerously personalised, reducing people to helpless victims so that the systematic failures of police, courts and governments escape censure. It's a problem sharply felt on BBC TV's Rough Justice. "We've had some success in getting convictions overturned, but in effect we're papering over the cracks," says Steve Haywood the series producer.
Taking Liberties, also from BBC TV's documentary features department, has attempted to focus on failures of the system - with some results. Last year's investigation into abuse of the Prvention of Terrorism Act was broadcast just before the Manx Parliment debated how to adopt it. Hazel Hannan, a member of the House of Keys, say the programmme influenced the debate, making amendments possible.
An analysis of stories on Taking Liberties over its previous two series shows it is most effective in catalysing some remedy to the mistreatment of an individual. But the result, if it comes, is often confined to the individual and there is no clear pattern of why it works for some and not others.
Television investigation has many practical limits. Most programmes of this sort are expensive and rarely last much longer than half an hour - short in terms of developing a complex arguement. In addition they are "one-shot" operations: it is hard to return to a subject once a programme or rival has "done" the story. New information is difficult to use after transmission, too. Newspapers, with their ability to follow up stories are better adapted to sustain the pressure that may bring about change. Politicians do not watch much TV, so programmes need press publicity - producers depend heavily on previews and reviews.
Chris Oxley, producer of Thames TV's Death on the Rock, says the trail that led to First Tuesday's trilogy on the Guildford Four began in 1982 with a piece he and Margaret Jay made for Panorama. "We showed that the condemnation of Anne Maguire could not be held up on the forensic evidence. The Home Office promised to look again at the evidence, but nothing came of it." It took another two years before TV was ready to tackle the story again.
Nowadays the climate for this sort of television is tough. Companies face the twin pressures of falling advertising revenues and competative franchises, with untried quality hurdles. Meanwhile the BBC is positioning itself for the expiry of it's charter in 1996.
In these conditions, broadcasters are careful not to get too unpopular, though most editors maintain that the attack against Death on the Rock has not affected their story choices. But Roger Bolton, controller of networks factual programming at Thames Television, says that more than ever there is an attack on the motives of people making independent television journalism.
Threats to originally researched investigations could come from a less obvious direction. Although the BBC regards Rough Justice as part of it's public service remit, bigger programmes are increasingly being funded with co-production and sponsorship. Grant McKee, head of documentaries at Yorkshire Television, warns of more insidious change. "It means that the priorities are no longer being solely set by British editors, and stories may need to have an eye on Ameican, Japanese and European markets."
The Author is on the production team of Taking Liberties. A new series started last night on BBC2.