Blossy obviously your brother didn't have his own policy of insurance, normally you can drive other cars and rely on your own policy, there are very few companies that allow you to drive all cars full comp,often when someone drives their own car they would be fully comp but driving others it might be only 3rd party so their insurance won't cover the damage to the car they were driving and the owner as in your case had to use his own insurance, your brother would only have been penalised for no insurance if he couldn't rely on a policy of his own.