Why a bigger excess won't reduce your insurance bill

There are some things we have always taken as read when it comes to car insurance: you're going to break the bank when you insure your teenage son, your insurer isn't going to like it if you leave your car in a crime-infested part of a city, and if you want to bring your premiums down, you simply hike up the excess you'll have to pay on every claim.

But at least one of these ever-present truths no longer stands.