First, the 3 year rule didn't apply in the first instance. Until 1968 the series was transmitted "Live" (i.e. not telerecorded). Each 50 minute episode was transmitted on Wednesday evenings 2000-2050. All we had were a couple of filmed OB inserts, partly to establish outside locations and partly to enable costume changes/scenery changes.In fact the very first scene of the first episode was filmed in a graveyard, where a police officer killed in the execution of his duty prompted the idea of two men teams working in cars (there were only two cars, Ford Zephyr 6s) The first episode was telerecorded off the studio monitor so that executives could gauge the quality of the script (and the show had writers of the calibre of Alan Plater and Elwyn Jones).
There were no car chases because there were not the facilities to record them in those days for TV drama. The programme certainly showed a more realistic side to police officers lives, because, unlike Dixon of Dock Green it showed policemen as ordinary men, not as some sort of patient saint. There was a hue and cry very early on when PC Steele (Jeremy Kemp) threw his dinner at the wall and struck his wife. Dixon would NEVER had done that - but real coppers did - as did, sadly, far too many men in those far off days.
The show was set in "Newtown" (not a very good name I admit), which was on Merseyside, but in reality the show was performed in London.
If you watch any TV from the 50s or 60s, the viewer in 2004 WILL be struck by the fact that it was all very studio-bound, very few exterior shots, except for establishing scenes on short filmed inserts as we did. Cameras were large and bulky so scenes tended to be more static and of longer duration. Funily enough, the budget for the BBCs sole soap opera at that time ("Compact" Tuesdays and Thursdays 1930-2000)was the same as ours, but whereas we tended to have larger casts and more sets, some of Compacts budget DID go on telerecording - the Tuesday episode was "live" and the Thursday episode recorded immediately after the live Tuesday performance). It was a case of either/or. Obviously we had to work within budgets and by todays standards they were miniscule but they were NOT cheap. As in any live work there were occassional fluffed lines, whcih you don't get today because you can reshoot a sequence time and again till it's perfect. By the way, with 'telerecording' you couldn't edit tape, so you were still performing 'as live', so only if there were to be a major catastrophy would you repeat because you had to record the whole show all over again (this is why the ATV/Central serial "Crossroads" got such unfair reviews - though a lot of the complaints such as wobbly scenery were untrue - it might happen once, and then, because the 'mistake' is repeated by viewers and critics people believe it always happened).
With respect, Ian makes the common mistake of comparing live or telerecorded TV from the 60s with todays sometimes overproduced TV. the comparison is neither fair nor like for like.
From 1969 onwards the programme was recorded on videotape/telerecording (VTR took over about 1971/2 but i had left by then). Later in it's life the show was turned into a twice weekly 'soap opera' style series (Mondays and Thursdays 1905-1930) and I believe it did then suffer a drop in artistic quality, though, of course with VTR retakes were possible so the technical quality was better: It really ended up as "The Bill" (ITV1) has now done.
One final point: our original Sgt (Twentyman) played by Leonard Williams only appeared in the first half dozen episodes. Len collapsed and died a few hours before transmission one Wednesday, so some hasty rewriting had to be carried out. He wasn't a famous actor, but did a lot of radio work including the long running comedy series "The Clitheroe Kid"