I think that's part of it. Coppers in cars tend to be ignored and while beat bobbies are likely to catch a crime in progress about once every 3o years people talk to them and they can act on the info.
It's amusing seeing people being arrested, I remember watching one of the "cameras in cars" documentaries with a mate. They were in Hull and Grimsby so we watched it for local interest. Most of what thgey were doing was routine teenagers with no MoT, a dodgy stereo and 10 quid's worth of dope, and the lads in question were yapping away, digging holes and hurling themselves in with abandon. "I never did noffin, you ant got nowt on me!" etc. They then cut to a car from out of town with 4 shady looking characters on board. Stop and check, they were from Birmingham with no reasonable explanation as to why they were in Hull at 10pm on a Wednesday. Silence. "If you can't give me an explanation of why you are here then I'll be asking you to accompany me to the station." Silence. 4 scowling blokes, not a word. There was clearly something going down but nobody was saying a thing. They didn't even ask for a brief. Off they went to the station, but they were a world away from the petty car stereo thieving local boys.
