An NCD is linked to a driver, not to a vehicle.
If, for example, you were to get rid of your first vehicle and only insure the second one, you'd still have your full no claims discount. So it follows that you'll still have your NCD for the second car. Indeed, since it would be best to put them on the same policy it would be impossible to have two different NCDs. (You'll be quoted a price for insuring both vehicles together, on a single policy, with the discount applied throughout).
There's no reason to assume that you'll notice any significant increase in your premium. Some people find that adding a second vehicle onto the same policy can actually reduce the premium.
Chris