my son bought a car last week and I drove it home for him.

all the way back from Cotswolds to other side of Reading. Just assumed that as the car wasn't registered to me, and I'm obviously insured to drive other cars under my policy I'd be covered.
Tax would be a grey area though. How are you supposed to tax it when the car isn't actually insured (bought it off a trader), and it's not registered in your name. Surely the law should be/is pragmatic enough to allow for this eventuality?
Anyway, got home ok with no incidents