When I first started driving many moons ago, my comprehensive insurance permitted me to drive other vehicles, but only with minimum 3rd party cover, for any type of vehicle for which I had a full licence, with the owner's permission. This only applied to the policyholder, not named drivers.
That would in my case have been such things as motorcycles with or without a sidecar, mopeds, three wheelers, vans or minibuses. Of course these would already have had to have a current insurance in the name of their owner. If I wanted to drive another vehicle which I owned, that had to have its own insurance policy. I think that more recent policies have restricted cover for driving other vehicles to ones of the same type, ie cars. These days, it is probably another chargeable "extra".
So if you have a car, and you are insured for cycling under its policy, does that limit you to a named bicycle with a specific identification such as a frame number, or does it cover you for any bike that you own? Many who post on CC will have several bikes, so it's not just a theoretical query.
Based on my experience at least, named drivers didn't get additional cover like the policyholder does, so would such a policy compare well for value for money compared with a standard car insurance plus a separate cycling insurance policy?
Just curious. it looks like it could get complicated.