’‘Nobody knows anything.” Veteran scriptwriter William Goldman’s famous description of Hollywood and its producers is as accurate now as it was then. But Hollywood is about feature films: huge, speculative leaps into the unknown, as risky as dropping an oil rig on to the floor of the North Sea (except films are more expensive and less predictable).

Television series are at the other end of the screenwriting business, and the maxims are different: “They know precisely what they want”; “Nothing else will do”; “Expect to keep doing drafts until they’ve got it”. Not forgetting: “It’s no good trying to be experimentalinnovativeradical - it’s a job”. (Save the great ideas for when, like Jimmy McGovern or Jack Rosenthal, you’ve paid your dues and earned the right to try a few things - usually after about 200 episodes.)

A series does not have a fixed lifespan. And it might be on three times a week, like EastEnders or The Bill, or it might come in 13-part seasons, like Casualty or Peak Practice. But a serial is finite - a self-contained story that reaches its conclusion after four, six, or 13 parts, such as Jewel in the Crown or Edge of Darkness (am I dating myself here?) or Our Friends in the North. Very occasionally a serial is so successful that it is extended into a second serial (Making Out or Twin Peaks) or converted into a long-form series. But, by and large, a serial is a story told in serial form; a series could in theory go on for ever (Coronation Street?).

The Americans seem to wipe the floor with us when it comes to something like sitcom, but British television is justly famous for the consistency and quality of its 30-minute series. And this consistency derives from a simple source: the writers are worked into the ground. Scripts are policed and revised and monitored and rewritten, and before that story lines are vetted and debated and only at the last stage passed fit.

American soaps - Channel 5‘s Sunset Beach is exerting a powerful fascination for me at the moment (but that’s self-employed lunchtimes for you) - are laughable, piling plot absurdity on melodramatic coincidence without a hint of embarrassment. British soaps (which are peak-time, not afternoon viewing) are more low-level drama, made entirely of the stuff of daily personal life, which usually requires the acting or the writing to be believable.

Of course, if some of the things that have befallen Albert Square were visited upon a real London street, it would be marked down as the unluckiest patch in the western world. But story lines have to be judged in isolation; no series can survive if you take a long-term view.

But, within the world of soap, there is an exception, a programme that begins and ends its story within each episode and which, even more extraordinarily, never features the personal life of its characters: The Bill. It started as a weekly 60-minute series, before becoming a twice-weekly 30-minuter. Everyone said it couldn’t be done. How could the writers possibly come up with more than 100 story lines a year?

The doubters have been proved wrong. The Bill now runs to 156 stories a year. But there is a price: it chews up writers, spits them out, and moves on. For the prospective scriptwriter this is good news: the programme has a vested interest in developing new television writers. For me, the downside is that, after a long run of episodes, I don’t think I’ve got another police story in me. I wake in the night howling, “734 from Sierra Oscar, receiving”. But it was a good training ground.

Jonathan Myerson’s recent work has included episodes of William Tell for Cloud 9 Productions. His first novel, Noise, is published in March by Headline Review and his animated version of The Canterbury Tales is due for release in October 1998