And also bear in mind two important factors:
1. Even though most do, not all Comprehensive policies allow you to drive other cars, regardless of your age. You must read your policy wording carefully. Comprehensive policies are so-called because they provide cover to the policyholder for accidental damage to his own vehicle as well as providing cover against Third Party risks as required by the Road Traffic Act. It has nothing to do with the cars you are allowed to drive.
2. If you are covered to drive vehicles belonging to other people you will almost certainly be covered only for Third Party risks. So, if you write off your friend�s Ferrari by wrapping it round a lamppost, you insurers will pay the council to replace the lamppost, but you will have to reimburse your friend in order that he may buy a new Ferrari.