I still occasionally drive on the motorway at 60 to keep fuel consumption to a decent level and have had people slow down noticeably as they approach me in the middle/outside lane. It doesn't happen as much as it used to though. Spotty kids in Renault clits still tend to get very paranoid if I'm behind them however.
I'm a bit of a sod for keeping left at all times too, which may have made some people suddenly observe the Highway Code. That and the hi-vis jacket hanging in view of the rear door window. And me wearing a white shirt.
Having said all that I'd wouldn't dream of impersonating the Police and never been remotely interested in being one either, but there has been a couple of occasions where I have flashed my lights in the Mig to warn others I am nearby and they've stopped their antics very quickly.
Probably the most amusing moment I had was when a group of about 6 marked Police bikes came barrelling up a dual carriageway and slowed down before rather cautiously overtaking me! I think they might have been on their way to being delivered or something as the rear beacon lights were covered up, but it was funny all the same.