It shouldn't do but it would depend on the insurer and how they feel about a second car. I have two cars insured under Admiral's multicar policy who were incredibly reasonable considering they're both fully comp, parked on the street, naming other drivers, used for everything, etc. They give you a discount the more cars you have with them. I'm also building up a new lot of NCB on the second car too.
If you're only going to use it when the 156 is in the garage you won't be using it too much so you're mileage will be rather low - I'm not sure if that affects policies much.
