If it's an "old" as in original MINI chalkie, then look at insuring it in your name on CLASSIC insurance and putting him on as a named driver. Nowadays named drivers also build up NCB and don't forget that ask for a fully comp quote first. The way that works is that insurers assume that if you ask for fully comp first then they see you as a more careful driver and lower your premiums considerably. If you ask for Third party only first you are deemed a higher risk and will pay for it. Try Lancaster for a start.
I'm with them for my 1972 Rover 2000 and pay £80 a year fully comp with not restriction on who drives, although you need to name to build up NCB.