THERE is little mystery surrounding the detective dramas being screened on ITV this summer. Follow the clues and it soon becomes pretty clear whodunnit - the schedulers whose lack of imagination has them filling peaktime viewing night after night with police series we've seen before. And seen not just one or twice but three or four times.

Viewers can be forgiven for a permanent sense of deja vu as Inspector Morse, A Touch Of Frost, Prime Suspect, Cracker, Inspector Wexford, Taggart and Midsommer Murders tackle cases whose gory details and denouements are only all too familiar to those watching.

Traditionally the summer schedules on BBC and ITV are padded out by re-runs described by continuity announcers as 'another chance to see' or 'just in case you missed'. They don't fool anyone, what they're really saying is 'this is yet another repeat'.

Some programmes can stand being shown and seen more than once. Comedy, classic comedy that is, remains funny no matter how long ago the series was made. The fashions in clothes may change but laughter is ageless. The BBC has successfully mined their archives to repeat endlessly shows like The Two Ronnies, Dad's Army, Are You Being Served? and currently Fawlty Towers which, to what must have been the acute embarrassment of bosses, attracted more viewers than any other BBC programme apart from EastEnders the other week.

Of course, the success of these classic comedies only serves to emphasis the sorry state of new comedy on any channel although it should be noted that even a recent series like Gimme Gimme Gimme, an acquired taste but one which some of us rather enjoy, is pulling in two million-plus viewers on its third screening in 18 months. The success of these comedies second (or third or fourth) time around may say more about the lack of decent programmes on any of the other channels than anything else.

Those who believed that cable and satellite channels like UK Gold were the home of repeats will have to think again. Sometimes the schedulers try to dress up the repeat of the repeat of the repeat. ITV's excuse for showing a dozen or so 'vintage' Inspector Morse episodes (does that mean the ones omitted are rubbish?) at peaktime Saturday night viewing is as a curtainraiser for the very last all-new Morse to be seen later this year. This makes it the longest trailer in the history of TV.

No such reasons are offered for the re-appearance of David Jason's Frost, George Baker's Wexford or Helen Mirren's Jane Tennison.

They aren't back by public demand but to fill in the gaps between the fly-on-the-wall documentaries and real life stories caught on camera. Repeats don't attract new viewers but, by and large, the same people that watched the episodes the first, second, even third time around.

Many fans will already have re-lived the finest hours of Morse and the others on video. They know whodunnit and why-they-dunnit, so quite what the pleasure is remains unclear. But - and this is where critics of these endless repeats come unstuck - the ratings are excellent. You can't argue with figures that show eight million or more people are tuning in to repeats of A Touch Of Frost, more than have been watching some new episodes of Emmerdale.

Prime Suspect is attracting seven million plus viewers and Morse's audience is a healthy six million plus. They are doing far better in the ratings than new dramas like the BBC's wildlife detective series Badger and the romantic drama Glasgow Kiss, which don't even make the top 30 chart.

Comparisons with new ITV drama are difficult to make because there is so little about during the summer months when viewing figures are lower than at the rest of the year because of the lighter nights and holiday period. Perhaps it's just the, some would say abnormal, fascination of the British for a good murder mystery that makes these repeats so popular but does anyone read the same Agatha Christie over and over again without showing signs of boredom?

There are plenty of other dramas that deserve another airing. It's about time ITV bosses had a rummage in their archives to find something other than old detective series to fill the summer schedules.