DETECTIVE duos are nothing new. They're a staple of TV drama, and the more mismatched they are the better. Compatible isn't a word in the vocabulary of the writers of such series.

Several pairs are added to the roll call of odd couples sleuths this month in new detective series. I say "new" although you'd be hard pressed to spot the difference to others of their police ilk.

ITV1's Murder City stars Amanda Donohoe as Detective Inspector Susan Alembic and Kris Marshall, the shiftless son from BBC comedy My Family, as her sidekick Detective Sergeant Luke Stone. They have, and I quote the press release, "two very different approaches to crime solving". You would expect nothing else from a small screen Holmes and Watson.

Alembic is "tough, methodical and also fiercely protective of her frequently misunderstood partner", while Stone "has an intense determination to get results by any means, however unorthodox."

In other words, they're like any other pair of TV detectives you'd care to name. None is actually called Chalk and Cheese, but it can only be a matter of time before someone makes a series with that title.

We've already seen Rosemary and Thyme, about odd couple gardening sleuths played by Felicity Kendal and Pam Ferris. You can't help thinking they thought of the title before the story. These gumshoes also conform to the rule that duos, whether professional cops or enthusiastic amateurs, should be physically as well as mentally opposites. This little and large approach works well, just as it does for those trying to raise laughs as comedy duos.

The point of another new ITV1 series, Murder In Suburbia, is that the two female detectives - one blonde (Lisa Faulkner), one dark (Caroline Catz), of course - "banter and bicker their way through every case bringing their own distinctive, though ultimately complementary, methods of crime solving to each investigation".

British detective shows are only following the example of their American cousins, such as Cagney and Lacey and Starsky and Hutch. These distributed the duties evenly. Not so much master and assistant, as equal partners.

Married couples are allowed, with sparring spouses in Hart To Hart and McMillan And Wife continuing the investigative battle of the sexes begun in the big screen's Thin Man series.

Only a few investigators are allowed to go solo, although even Columbo always had his dirty mac by his side. His creators gave him so many little quirks there was nothing left to fill out the character of a sidekick.

But Inspector Morse had his loyal Sergeant Lewis. If you couldn't identify with a poetry-loving, opera-going, real ale drinking detective, there was always his plodding Geordie assistant to root for.

A Touch Of Frost's Jack Frost has had a succession of helpers, the most recent being a nave geography graduate. Good, observed Frost, the new boy would be able to find his way to the canteen to get him a bacon sandwich.

Frost remembered that sidekicks are expected to be treated with contempt most of the time. Witness Moonlighting in which private eyes Maddie Hayes and David Addison spent more time sparring verbally than solving crimes.

Partners are permitted to be nasty to each other from time to time and fall out (usually over a woman/man), as long as they make it up in time to end the episode hugging each other.

Sometimes a sidekick will get fed up being patronised by his boss and leave. Replacements are usually outsiders appalled at their new posting. With Troy's departure for a new job up North, Midsomer Murders' Detective Chief Inspector Tom Barnaby has welcomed new recruit DC Dan Scott. This city boy looks like he does male modelling on the side and was clearly less than impressed at being posted to the English countryside. If he expected life in Midsomer to be sleepy and uneventful, he's had a rude awakening. There are more dead bodies to the acre than anywhere else in the country.

This week saw the return of the crime-busting duo in The Inspector Lynley Mysteries. This teams up a posh detective with nice suits, nice car and nice accent with a petite, common policewoman with an accent out of EastEnders and the dress sense of Nora Batty. This pair amply fulfil the requirements for ill-matched detective duos. He treats her badly, she solves the cases - not a fair distribution of work, perhaps, but viewers seem to like it.

Conflict is at the heart of duos. Maybe it's something as minor as Starsky liking junk food and Hutch opting for health foods. Dalziel And Pascoe, with its bluff Yorkshire policeman partnered with a sensitive, sociology graduate, reflects the duo at the heart of The Streets Of San Francisco. There, Karl Malden's Mike Stone favoured tried and tested methods whereas partner Steve Keller was a college graduate more likely to employ modern ways of detection.

But, perhaps the most unusual TV detective duo were Randall And Hopkirk (Deceased) - one of them was a ghost.

l Murder In Suburbia begins on ITV1 next Saturday at 9.15pm and Murder City at 9pm on March 16. The Inspector Lynley Mysteries continues on BBC1 on Thursday at 8pm.