Had a chat with the traffic officers involved with this new enforcement.
Apparently all cars should at point of manufacture read below 82db (TVR?) and are tested.
The police (Devon and Cornwall are trialling) now carry noise testers which are used if and exhaust sounds louder than standard. Cars need to be below the 82db, some 4X4 are allowed 89db. The test is at 3/4s of the rev range and if you fail it’s a £30 on the spot fine, no points. However if you get caught and fail again then its off to see the judge who will in the officers words ”dish out a larger fine”. I asked about the VDF but its only the fine, this seems odd to me. If there is something a miss with your car you should be made to rectify it.
So anyone with an aftermarket exhaust is likely to get a fine, me included. I asked about passing an MOT and he said it at the tester discursions, since my brother in-law sorts mine I’ll be ok
Hope this helps?