As
Verity touched on you can't use NCB on more than one vehicle which meant when I got another car last year I thought life was going to get very expensive!
Found Admiral multi car came out well and even made it worth cancelling policies I had in place based on cancellation charges to move all policies.
Just got a Cali Ocean which I added onto the policy with 8K miles and Buisness. With the additional discount on the other 3 cars already on the policy cost me a total of £8 for the next 9 months. Without business they would have paid me £1.35!! Was shocked but happy.
Just hope that there are no big shocks when it comes to the renewal.
Other thing to note when I was searching around last year for insurance I found it cheaper to have 8K miles than 2 or 3k miles.