This is the thing with insurance companies, its a win win, have all the cake situation.
If you ride a bike and have X years no claims they cannot be transferred or account for anything in terms of car insurance and visa verse.
If you have an accident on a bike and make a claim, it also effects your car insurance.
R1 Loon explained why, but seriously it really is a win, wind; eat all the cake situation for insurance companies.
So forget your motorcycle or NCB on motorcycle insurance as you going to have to swallow the premium on a van, which ain't cheap even with 5 years no claims let alone 0.