In theory a car in a lower insurance group should be cheaper to insure than one in a higher group, but insurers factor a large number of variables when providing a quote. Insurance groups are decided by the Association of British Insurers and Lloyds Market Association, and vehicles are assigned groups when they first go on sale. However, any insurer will also apply their own risk factors to the vehicle as well as taking into account the insurance grouping, so you could obtain another quote on the same two vehicles from a different insurer and may have a different outcome.