It is a real problem when there is nothing but a single reading that someone is prosecuted on. I would tend to suspect that a grey import Subaru Impreza could have had a tampered speed limiter.
Later on in the article it mentions a 1.2 litre Fiat Punto that was clocked at 115 mph while its top speed was 104 mph. Fiat Puntos aren't limited, so a mod
that could add 11 mph would be a load of work and that case looks more like a speed gun error.
The problem is that individual conviction thrown out doesn't prove inherent inaccuracy of speed guns. The police and speed camera makers can say what they like, because it will cost far more to fight a conviction than to pay up. I know, I've been there, and I will never, ever, get out of the way of an ambulance again. I simply can't afford to pay £900 pounds in legal fees again for trying to help for a few seconds.
All the times I moved out of the way for emergency vehicles, left rubber on the road stopping when one pulled out, and they wouldn't even admit where the ambulance had been to help may case.
I realise that the police see far to many accidents and loads of drivers pull all sorts of tricks to speed, but there are a lot of doubtful convictions.