Pass Plus is normally just a discount, if you stay with the same company on renewal they normally give one years NCB plus extra Pass Plus discount to make it equivalent discount as 2yrs NCB (as long as you dont claim that is lol)
Norwich Union gave me a 52% dicsount for doing Pass Plus, but then I had an accident, lost my discount, and was quoted over £3k at renewal. But by this time, I had blown my engine and didnt need the renewal.