Hello Mikey
On what grounds would the police prosecute? Provided the trailer weighs less than the cars specified max towing limit, then what offence has been committed?
You cannot be prosecuted for an over weight trailer provided it complies with the towing vehicles specifications, However, if you are stopped for having an unsafe outfit, then the reasons for it being classed as unsafe must be more than simply the weight of the trailer.
There is a situation where more than 100% ratio is illegal, and that has nothing to do with the car, but the drivers licence categories. There was change in the licence laws in Jan 1997. Before that date all drivers were awarded category B+E. but post 1997, all driver are now only awarded Cat B, which limits the fully laden trailer to 100% or less than the kerbweight of the car. The other important factor is that the combined MAM of both car and braked trailer must be 3500Kg or less.