Disabled son of 22 with licence for 3 years looking to drive at most twice a month

Is the university your son goes to near where you live? If it is far away, then you can look into short term car insurance if he's only going to drive when he comes back home from university during holidays. Otherwise it probably makes more sense to have him as a named driver on your policy as he won't be using your car a lot as you will therefore save on car insurance premiums. I suggest however that you look at an insurance company which will give him discount as a named driver so that when he takes out a policy in his own name, he doesn't start back to square one, that is, with zero no claims bonus.