Driving Other Cars
Most policies cover the policyholder to drive a car belonging to someone else (with their permission), but it is important to note that cover will be restricted to third party only even if you have a comprehensive policy. You will not be covered for accidental damage to the borrowed car.

It is much more advisable for the owner to arrange comprehensive cover for you under their policy. If they do this then you will be covered for accidental damage to their car.