It is interesting to know that there are 20 groups for car insurance. Each type of car is allocated to a group and those in group 1 attract the lowest premium and those in group 20 attract the highest. Cars in the lowest group include a Fiat Panda and Vauxhall Corsa and the highest group would be things like a Porshe 911.
There are a selection of reasons why cars are placed into certain categories. These are things like the cost of the parts, the repair time, the performance of the car, how good the car security is and the new car values. A foreign car is likely to be more expensive to repair because the parts will be more expensive and harder to get as will a vintage car and so these are likely to be in a higher category than a British car which has parts that are easy to get hold of. It makes sense that cars that are more expensive and time consuming to fix will attract higher premiums and those which are cheaper to fix will be cheaper to insure.
If you are buying a new car and want to keep the cost of insurance down then it could be a good idea to look on the Association of British Insurers website to see which groups certain cars belong in and this might help you when deciding which car to buy. It can make quite a significant difference to the cost of the insurance. Remember that you will have to pay insurance every year you have the car and so a small saving each year could really add up over the life of the car. Obviously, many people want a more powerful or bigger car but it could be worth looking in to the car insurance groups if you are choosing between models.