My uncle got his amateur radio callsign (G4 ODM) at an auction a few years back - I think he paid the starting price of around £250, which includes the transfer fee. His son, at the same auction had to bid against somebody for his - I forget what his callsign was but I don't think it was obviously valuable.
For anybody interested, all UK registrations tell you where the vehicle was registered. The new ones are more obvious - H?03 ABC is Hampshire, L?52 ABC is London etc. The 03 or 53 is for 2003, 02 or 52 is 2002 etc. The older ones (pre 2001) are more difficult - again two letters the town/city but you need to be a nerd to pick them out (I know a few!). Eg. for J123 DAP the AP is Brighton. My car J758 LRV was registered last year in Portsmouth (RV) - but because it was imported and manufactured in1992 it is issued with an old registration number. Portsmouth also has BK and a few others. Vehicles registered in the Isle of Wight (through Portsmouth I think) have the letters DL.
This is probably the most comprehensive list I've found.
I smirked at my boss's hire car today - CL52 JFK.
Gareth