Originally Posted by Flamin_Squirrel

It works the way it does because you take your insurance cover out for a fixed period of time.

Over a year, person A might be 5 times a greater risk (perhaps in terms of age, NCB, whatever) than person B, but person B might do 5 times the milage. They will pay the same premium because the risk the present to the insurance company is the same, and that's all their interested in. Making sure they've earnt enough money from you by the time you're expected to make a claim.