With the stealth van on the Snake, I've always been really tempted to mountain bike in and slash their tyres whilst they're sitting in the back on the camera
Worth remembering the usual cutoff for prosecution is 10% + 4, ie 59 in a 50, 37 in a 30 etc.
I have had points for both 37 in a 30 and 59 in a 50 (Snake Pass)
Having said that, when coming into town on Ringinglow Rd that light-up 30 sign only comes on if you're doing 38 or more.
I heard it was 10% plus 2, but to be honest I don't believe it is anything hard and fast, could just be an urban myth. I'm sure they could and would bust you doing 32 in a 30 if so inclined.
In a departure from the usual large saloon/estate unmarked cars, South Yorkshire Police are now running a silver Focus RS/ST/whatever. I've seen it nicking two people over the last 5 days, one at M1 J33 and one just round the corner from home in Norton.