most uk circuits are 105db or 98db depending on location, it is pretty loud for a car. maybe the silencing has had enough. try another back section or fit a second silencer. if your noty convinced with the police reading, get it checked independently.
to give you an example of how easy it is for the noise to go up, i was at a trackday (105db) with my 250.. from cold it was over 110db. after it reached temp and i stuuffed rags in the lower fairing it sailed through at someting like 99db. my point is, if the baffles are tired it could easily effect the noise output. esp with db reading equipment.