Scotty15 and Battenberg are absolutely correct (did anyone ever doubt it?)!
I purchased 2 x JWH 100070 "Bulb - Dial Illumination" bulbs from my main stealer today - cost £2.24 each (NB I can't find these on the web anywhere other than Rimmer Bros who don't display the price in their online catalogue).
I had two bulbs gone, one in the right-hand rocker switch, and the one which illuminates the little buttons across the bottom (I could live with one bulb being out, but 2 needed attention!).
Out with the radio makes it easier for me (2 allan screws on my radio), then rest the radio on the dash (without disconnecting, so no need to mess with the security code). Then fingers down the back of the dash to loosen the clips for the aircon unit and out it pops. Once out, there are 3 connectors to remove (they're all different so no need to label them).
Once the unit's clear, you can see 2 x cross-head brass-coloured screws which loosen easy. Then the first PCB hinges out of the way (it's connected to the second pcb by a ribbon cable). You don't need to undo anything else, just remove the bulbs with a sharp screwdriver, and put the new ones in place.
Total time 15 mins, job done...
Works a treat!