I believe you are referring to the classifications of cars that is done in the UK by the Association of British Insurers (ABI). In the UK new models of motor vehicles are given an insurance group rating which insurers find helpful as one of the ways in which they determine a driver's premium.

Insurance companies classify cars so that they can provide the correct level of insurance. To do this they assign each car to a group between 1 and 20. This is done so that each model of car can be accurately banded with cars of similar characteristics. There can be a significant spread of groups within a particular model range.

The higher the group, the more relatively expensive it is likely to be to insure the vehicle thus 1 is low, 20 is high. Most family cars fall into groups 6 to 12, unless they have high-powered engines. If you have a sports car, or high-risk car then the group rating will be higher. So idea is that the lower the group rating, the less your insurance premium will cost.

For examples of group 3 and group 6 cars lets look at Volkswagen. In group three there are VW's, Polo's and Lupos while in group six there are Boras and Golfs listed.

Factors used to calculate group ratings include the following:

• Damage and Parts Costs - The likely extent of damage to each car model and the cost of the parts involved in its repair. The lower these costs, the more likelihood there is of a lower group rating.
• Repair Times- Longer repair times mean higher costs and the greater likelihood of a higher group rating.
• New Car Values -The prices of new cars identify the higher specification models within a model range.
• Body Shells - The availability of body shells (the basic frame of the car) is taken into account in group ratings because they are essential for certain accidental damage repairs.
• Car Security - Security features fitted as standard equipment by motor manufacturers can help to reduce insurance claims costs. Such features include high security door locks, alarm/immobilization systems, glass etching, coded audio equipment, locking devices for alloy wheels and visible VIN numbers.

You can look up the group rating for cars at the Association of British Insurers (ABI) site but keep in mind that these group ratings are recommendations only. Individual insurers, depending on their own experience, may vary from these recommendations.