Media: Someone's stealing your ratings? Call in the police: John Dugdale investigates the case of television's endless appetite for more crime series

THE film Headcase is billed as a 'story of sexual intrigue and forbidden passions', but today's schedule for Imogen Stubbs, playing the private eye, Anna Lee, is more mundane: waving away a would-be windscreen washer at a red light, driving her clapped-out Sunbeam Alpine through Kensington, breaking down in hooting traffic. The first shot alone takes three hours to get right.

London Weekend is shooting a two-hour pilot for a projected series centred on Stubbs's spunky young crime-buster. A few weeks ago, another LWT sleuth, a Jewish cop named Sam Sterne (played by Ivan Kaye), made his ITV debut in Sam Saturday.

Do we really need two more television detectives? Nick Elliott, LWT's drama controller, sees 'no sign yet that we're overdoing it'. Verity Lambert, the executive producer of Sam Saturday, says 'there's room for some new series on ITV because they aren't making any more series of Inspector Morse or The Ruth Rendell Mystery after this year.'

Over the past five years, ITV has established itself as the dominant network in prime-time crime, with a dozen shows regularly pulling audiences of more than 10 million. An important element in this success is the federal character of the commercial system, which encourages drama bosses to find and adapt crime fiction set in their own regions, the most recent success of this type being Yorkshire TV's Heartbeat. Another factor is the policy of bagging the best 'classic' detectives: Holmes, Poirot, Maigret. The BBC has had to make do with Miss Marple or the wooden fantasy-heroes of Margery Allingham and Ngaio Marsh.

But the departure of Morse and Wexford will leave a big gap, and other long-running series must soon flag. Mr Elliott identifies a further problem: 'ITV's leads are all creaky old men. If we're competing with Sky, we've got to appeal to young audiences - I'm not talking about kids, just people in their thirties who don't identify with figures such as George Baker and John Thaw.' Hence Anna Lee and Sam Sterne: both played by attractive thirtysomething actors, both leading what LWT publicity calls 'somewhat disordered love lives' ('you don't get any sex in Morse, but you will in this', promises Andrew Davies, the adapter of Headcase).

At the BBC, the position is far more desperate. The drama department currently lacks both a costume detective series and a mainstream police series, and a number of its 1991/92 launches (including the intended replacement for Bergerac) were flops. There were some successes in the spring season, but they were three-part serials or single films, when what is needed is a 'banker' show which will secure high viewing figures over at least 10 weeks of new episodes and repeats.

The necessity of a counter-offensive has been recognised. When the BBC governors made an extra pounds 40m available earlier this year for popular programming, Michael Wearing, head of serials, said he would devote much of his share to 'three new mystery series'.

With the BBC frantic for a hit, and ITV keen to replenish its portfolio, those involved in producing or publishing detective fiction are enjoying a bonanza. Most writers who figure prominently in bookshop crime sections have been optioned for television dramatisation, normally in deals which give the production company the right to develop new storylines using the authors' characters. Sam Saturday is unusual in being an original concept: the majority of police or private-eye series are adaptations.

Shopping for the right crime writer to adapt is a tricky business, as best-selling authors (Dick Francis) may not work, and authors with unimpressive sales figures (Colin Dexter, author of the Morse books) may come off spectacularly.

An obvious option is another quirky middle-aged cop pounding a rural or provincial beat - Yorkshire has high hopes for R D Wingfield's scruffy Jack Frost, played by David Jason. But other companies have chosen to buck the formula by plumping for so-called 'new crime'. This marketing label is sometimes applied to the output of a group of writers - including Liza Cody, Sarah Dunant, Mike Phillips, Mike Ripley and Joan Smith - who have emerged since 1985. Their leading characters are youngish, and usually live in London. Social issues - race relations, corruption in Docklands, animal rights, terrorism - are prominent. In the novels of Dunant, Smith and Cody (creator of Anna Lee) the detectives are women.

But will such writing have audience appeal when translated to the screen? Inner-city locations, oddball sleuths with bohemian lifestyles, plots without puzzles, feminist or quasi-political themes - all the standard ingredients are bound to alienate fans of the old-fashioned whodunnit. Although 'new crime' detectives may well attract a different sort of viewer, it seems unlikely that they will ever deliver the phenomenal ratings achieved by Morse and Wexford. There is a mismatch between the kinds of story that younger crime writers are producing, and the kinds of story that mass audiences (and hence television executives) want.

The most popular series tend to be set in the past, or in parts of the present-day world (such as Morse's Oxford or Wexford's imaginary Kingsmarkham) which are cordoned off from Nineties reality. The heroes are stoical, substantial figures, representing the values of an earlier era. Viewers clearly distrust trendiness and gimmickry - although this applies not so much to the writers above, more to the numerous proposals in ITV franchise bids for shows with New Age, hi-tech, ethnic, green and geriatric gumshoes.

Contemporary messages are tolerated in mini-series such as Prime Suspect, but the allure of the detective series that stretch across the autumn and winter seasons is primarily escapist. Their appeal is akin to that of the accounts of domestic poisoning cases in the News of the World in the Thirties and, indeed, there is an obvious parallel between the inter-war era - the 'Golden Age' of English detective fiction - and today's literary and televisual crime boom.

Mr Elliott sees no prospect of viewer fatigue, and points to other factors underlying the popularity of crime drama: 'It's a model form of story-telling, with a beginning, an ending, and a moral outcome. And those who say there are too many detectives on television perhaps forget that a lot of the ITV and BBC 1 audiences outside London don't know a whole range of people - my mum said she couldn't relate to the dealers in Capital City. But every town has a police station, everybody has met policemen. There are no problems in relating to them.'

(Photographs omitted)