Another nice little earner dicovered by NuLabour to support their spend, spend, spend culture. I can't see any connection between having dirty windows on your car and domestic violence, but maybe their think tank has come up with the idea that people with dirty windows are more likely to be husband / wife beaters.
Without the money Nulabour make from car owners in one way or another this country would have to cut back severely on lots of Nulabours Loony schemes.
Any money made from motoring fines should be spent on our sadly neglected road network, (but then so should road tax, but it isn't).