I've just gained a 2nd car too and have had games with this. Some places just tried to screw me over on insurance on the 2nd car. Even tho we only wanted to do very small millage i.e. 3K they came out with silly quotes due to having 0 NCB on it.
Admiral on the other hand were great. Due to my 'good record' they mirrored my 10 yrs NCB from the 350z to the Mini. The quite was VERY good, less that thier normal quote pretending to have 10yrs NCB. They also said any accidents on one car does NOT affect the NCB on the other which is great. Thier renewal price for in a couple months time on the 350z was also VERY good, in fact lower that last year which is good considering overall prices have generally gone up recently.