Thats correct, your NCB can only be applied to one policy.
I had the same issue when I first started running 2 vehicles - luckily my first 'second' vehicle was a classic landrover so its insurance was cheap even with 0 years NCB. If you've had a company car, then they sometimes will allow you some NCB against that policy, but you'll need to shop around to find the best deals - you'll find some 'multicar' policies are actually more expensive than two separate policies. If you're of a certain age, Saga (don't laugh) are very competitive for unmodified vehicles
