Cars are assigned to one of twenty "insurance groups" by the Group Rating Panel,
which bases groupings primarily on research conducted by the Motor Insurance Repair Research
Centre (Thatcham). Not all car insurers choose to use the groups set by the panel -
some opt to set their own groupings instead. The factors used to calculate group ratings are:
damage and parts costs; repair times; value; availability of body shells; performance; and security
Whichever set of insurance groups an insurer works to, you'll typically find that cars
in lower insurance groups attract a lower premium whilst cars in higher insurance groups
attract a higher premium, usually because they are high performance models or prestige cars
that have high repair or replacement costs.