Thatcham is implementing a change which will increase the number of insurance groups from 20 to 50 in the next 18 months.

Insurance groups were introduced 40 years ago to give a risk advisory for insurers, and are based upon repair costs, performance and the car’s value.

Thatcham increased the number of groups from nine to 20 in 1992 to take account of factory fitted security devices, but a changing market has left the system unable to adequately distinguish between vehicles. The new system will rate cars based on additional criteria to give a more accurate reflection of their insurance risk.

Repair costs will examine the use of specialist materials or techniques, while the list of commonly damaged parts has been increased from four to 22. Performance potential will look at power output, acceleration times and the torque/weight ratio of diesels to give a more appropriate figure.

Thatcham is also incorporating weight into its changes. Testing has shown that heavier vehicles tend to result in larger third party claims, particularly 4x4s which usually sustain less damage than they inflict.

Some insurers are already using 50 groups, but the old ratings will still be available until it has been fully implemented, a task which Thatcham hopes to have completed by July 2008.