IT IS not, it has to be said, the most appetising of prospects on paper. A new cop show starring Nick Berry. Indeed, it's hard to think of which element is the more off-putting. After all, Berry's recent track record - in the criminally bland Heartbeat, in which he played a policeman, of course, and the merely criminal Harbour Lights - hardly inspires confidence. And it's not as if we're running short of crime drama on the small screen.

So, Peter Jukes could have been forgiven for not getting too excited when he first heard about the idea of Berry appearing in a programme about undercover detectives. ''Basically,'' he admits, ''I said 'Another cop series? Oh, no'.'' Which could have been a problem since Jukes was being asked to write it.

The fact that In Deep debuts tonight, proves that Jukes managed to get over that initial reluctance. ''I did a bit of research and I discovered that there's very, very little known about how undercover works - the procedures and so on - and I thought maybe there's a journalistic thing to explore. And as soon as I started thinking about the metaphors of a double life - your work, your home - I thought this could really be interesting.''

In Deep charts the lives of two level III undercover detectives, played by Berry and Stephen Tomkinson. Level III indicates those detectives who are ready to assume an identity and maintain it for perhaps a number of years - a process that can inevitably pose problems for the policeman's well-being, particularly if he's going home to a family at the end of the day, as Berry does in this series.

''The psychological dangers are great,'' Jukes agrees. ''They can't talk about their victories or their disappointments. They are often flashbacking. And I just wanted to feed that into the story. I wanted to show that there's as much drama going on in their home life.''

If nothing else, Blue on Blue, the first of three stories, certainly allows Berry the chance to shirk off his nice-guy image as a cop who's prepared to kick seven shades of shoeshine out of his partner to ensure their operation is not compromised and to

have his daughter's new boyfriend arrested for keeping her out late.

That said, the subject of police corruption which provides the plot's motor does offer rather meat-and-potatoes thrills, as Jukes is the first to admit. ''The first story is the more conventional one to let the audience get used to these rather warm actors playing unusually tough parts.'' The subsequent dramas promise to be much edgier as they tackle such uncomfortably timely subjects as the investigation of a paedophile ring and the infiltration of a group of racists.

Unsurprisingly, Jukes found the police a tad reluctant in helping him in his research. ''I was getting nowhere through the official channels, but I found two unofficial channels which, obviously, I can't reveal. They took me out to show me the procedures. They weren't operational undercover officers at the time, but they had been or else they were backing up other officers. They knew the whole routine.''

Field research even entailed tagging along on a couple of ops. On one Jukes went on a long surveillance of drug-dealers which ended with him sitting behind the two targets in a pub.

When the policeman he was with went out to get back-up, one of the targets turned

to Jukes and said: ''I f****** know you. You're a f****** police officer.''

Exit Jukes left, at some speed. ''As I got to the door the guy who was running the operation said 'Hold on Peter. I'd like you to meet my two mates. It was all a set-up. They wanted me to feel what it's like to be fronted up.''

Jukes started writing at university where he was a contemporary of Tilda Swinton and Simon Russell Beale. His first professional writing was mounted at Edinburgh's Traverse Theatre in the late eighties, but the appeal of playwriting soon palled.

''I was sitting in the theatre thinking that everybody in the audience was a practitioner - a director or an actor - and I thought: 'I want to get a bigger audience, people like me when I was a kid who had no culture, who never went to the theatre.''

His early experiences of writing for television were hardly encouraging ones, however. ''I was in development hell for years and all my best stuff didn't get made.'' These included a drama about political lobbyists, for which he had shadowed Ian Greer, spiked two years before New Labour came to power and the issue came to prominence. So discouraged did he become that he had effectively given up on TV when Mal Young, the BBC's controller of continuing drama series, approached him with the idea for In Deep.

Jukes's next projects are not quite so pre-packaged. He's working on a screenplay for the BBC set in a Young Offenders Prison and a drama series about the origins of psychiatry. But he's not done with crime drama. He's working on a new series of the Trevor Eve vehicle Waking the Dead, and, given the chance, he'd like to do more In Deep. ''It would be nice if other writers got the chance to write for it as well. That's one thing I regret in this country. There isn't that team writing like you have in

the States. They have the ability to collaborate.''

Of course, that's a notion that goes against the grain in British television. The models of Bleasdale and Potter loom large. Outwith soaps, there's always been a preference for the individual writer giving us his singular vision. ''But I think that's led to writers being powerless and then overpowerful,'' Jukes argues. ''Writers get powerless because they're not in the production cycle - they're just dialogue providers. Then, when they do get production power, because they've been squashed and abused so much, they overstep the mark.

''British TV is trying out the American system now with writer-producers and that's the way we're going to match American TV which has overtaken us. I learn more from good American shows like The Sopranos and ER than I do from watching British shows.''

l In Deep begins tonight at 9.05pm on BBC1 as part of the Crime Doubles season.