I would get the MOT station to send an invoice to the ploice station for having them test ur exhaust, just cause the WPC is having a bad day and doesnt have a clue doesnt mean you have to foot a bill. I hate when stuff like that happens who's to say the WPC can tell when an exhaust system is excesive, i dont see any certification of training.
Bloody terrible, im just having a bad day BTW