The Bill: Britain's most famous television police drama is almost an industry in its own right

A young copper is brandishing a piece of police equipment, as he reasons with a heavily-armed adversary, sporting a bandana to obscure his face. Given today's crime statistics, it's probably not an unfamiliar sight for residents of the tougher estates in south London.

But this is not a Metropolitan Police crackdown on the Aylesbury Estate in Walworth, but a rehearsal for a scene in The Bill, TalkbackThames' serialised drama, which celebrates 25 years since its first episode this month. The fact that it is hard to tell the difference between fact and fiction is a telling tribute to the programme makers' obsession with realism.

The implement being brandished by Alex Walkinshaw, who plays Sergeant Dale 'Smithy' Smith, is an extendable baton known as an ASP, currently employed by London's police force. Walkinshaw is also wearing a real Met uniform. Chances are, if it's kit the real boys in blue are using, you will soon see it on your television screens.

The Bill began as a pilot on 16 August 1983, with the first proper episode being transmitted in October 1984. It started with one episode a week with hour-long separate storylines for the first three seasons, but for the last 10 years has been serialised. It is now broadcast twice a week on ITV.

"Everybody felt the audience had to get to know the cast better," says the show's executive producer, Johnathan Young, on the decision to serialise the show. "We are still refining that. The most successful serialised stories blend the personal lives of the characters with their policing. It is fast-paced, like all television nowadays, but it is still true to the original brief of the programme. It is about ordinary people putting on a uniform and being at the front line of dealing with the ills that face society."

Young says he thinks the secret of the programme's success is simply just how real it is. Each of the show's "departments" has its own strong links with the police, whether through the researchers, the scriptwriters, make-up artists or set designers. "The designer will come to us and say, 'Do you know that they've got new radios?' And we will talk about getting them in for the show. We try to keep it as up to the minute as we can." However, he is keen to stress that they are not "editorially bound" to the police force in any way. "We met [head of the Metropolitan Police] Sir Ian Blair two and a half years ago and he said there was no need for us to have a closer editorial relationship than we do. We take the view that we find it a privilege to represent the Metropolitan Police on screen, but we read the papers like everyone else and know the cops are human."

Young says those who watch The Bill identify with its characters in a more "real" way than they do with those of other series. He adds that the scriptwriting team is currently debating how far they can go with a story about post-natal depression. "You'd be really cautious about something directly related to, say, [the disappearance of] Madeleine McCann," he adds. "We have a constant dialogue with people at ITV to make sure there is no cross over. To see such a thing regurgitated in a drama looks cheap and exploitative. It is unnecessary. You would even be cautious telling something where the names were changed."

The secret of the show's success is an in-depth understanding of the relationship between the characters and the target audience. "It is all about the characters; Smithy is a brilliant example. He puts on a uniform and takes on the burden of society to do good. And that makes him heroic. But he is a flawed hero, too, and that is very attractive. What we do best is when we talk to the cops, who see things first, then we get back to our drawing board and put it straight on the screen. That makes what we do exciting to an audience."

When filming around south London, does he ever feel people take offence at their homes being depicted as the kind of place that would attract crime? "It is less problematic than on other shows. Our cast are used to dealing with the public. They are good at talking to people, and will let the public take photographs of them. We generally operate on a low budget and, by and large, use hand-held [cameras], which we use to make the show as real as possible. We filmed on an estate in September for an eight-part series and stayed there for three months. After two weeks, there was a bit of a 'what are you doing here?' incident but by the end of our time there the cast and crew were sorry to leave."

The show's makers are glued to American television screens, where some of the most exciting crime drama is being shown.

"It is a different kind of show," says Young. "In the US they have raised the bar. There are things which we see on those shows that are brilliant. They are brilliantly written. But they are not about what it is like to live in Britain in 2008. When they portray their own worlds they are fantastic. And they inspire us, to be honest."