Police trial an automatic tread depth reader

I have heard on the radio that police are trialing an automatic tread depth reader. They unit is put on the road, the car drives over the reader and if your tread depth is below the legal minimum (1.6mm) 100 yards up the road you are pulled over by the police. The penalty for an illegal tyre is 3 points per tyre and up to £2500, remember this is per tyre not per stop by the police. 4 illegal tyres and you will be off the road. So keep an eye on your tyres because getting replacements before you are illegal is cheaper and safer.