You pose what is possibly an unanswerable question, I reckon. :|
Logically, your insurance will rise as you are now insuring two vehicles not one, and gaining the benefit of the NCD on the car is probably going to be the best option. Again, logically, your mileage on the bus will drop significantly, so a limited mileage policy ought to enable you to get a good deal from any of the main players, probably better than your present deal even without NCD. Whichever way you play this, you can't escape the fact that you are insuring two vehicles now, albeit you can only drive one at a time of course (unless you have a second named driver...there are so many variables to insurance that it is virtually impossible to answer this sort of question in a forum). Maybe enquire about a multi vehicle policy, although I have now found these to be economical personally? Good luck, and do tell when you find when you make enquiries.
Kev