Bejabers, I guess it was an interesting question after all...! Nothing will start a riot like a linguistical opinion - it's the same over here. For obvious reasons (ja ja) I won't enter into your discussion, but you may all rest assured that listening in on your debate is very informative for me.
Several of you have mentioned or implied the police forces, and now that you do, it does remind me of having heard this kind of idiom emerge from underneath a bobby helmet (on television.) The Artful Dodger and the character from Porridge (a book? teve-series? musical?) also confirm the concept for me and make me feel that I'm on the right track. My character knows a lot of knowledge too, and dodgy he is!
The Morecambe and Wise Show was on here a hundred years ago - that may actually be where I first noticed it!!
Thank you all so very much from me and
Sherlock