Reg 100 & MV(DL)R reg 43 Construction and Use Regulations state
A driver commits an offence if they use a vehicle in a such a condition that anything on or in the vehicle or any accessories or equipment, or the number of persons carried in or on it the vehicle, are likely to cause danger of injury. and that is about it.
The regulations are open to interpretation and sometimes comes down to personal opinion, and this could include overwight issues as well, so a judgement call has to be made by the rider before they set off.
i know that, but i thought that if you did have them on then they had to be usuable?? like the seatbelt law if if fitted must be worn and in working condition blah blah