I had a classic quite a few years ago. If I added the wife to my policy it got cheaper. Best thing was she only had a provisional license!
The explanation was that when adding your partner you left the car at home for them to use, they didn't, and overall had less accidents.
Under-standable, but as she couldn't drive anyway how they came to this conclusion was beyond me.
Tell you what love, I'll leave the car for you that you can't drive and go walk for the bus in the pissing rain shall I? Crazy.