In my communications with the PVEC regarding the legality of running with blue lights, I got in touch with somebody who is trying to persuade the owner of a Birmingham City Police Car to join them, and I can only assume that this is one and the same car. I have no other details apart from that - if you have any further questions that perhaps he may be able to answer I can forward them on for you.
I have a book called Mini & Mini Cooper,Colour Family Album, in which this car features. Apparently owned by (then) Edward Armstrong, page 12, ISBN 1-874105-79-0. It's probably on Amazon if you want to have a search for it!