I just replaced mine,remove the black trim from the silver surround (2 screws on top ,3 screws underneath)you should then see 1 silver screw at either end which holds the front fascia on.you will then have just enough clearance to remove the 8w fluorescent tube.i didn't have to fully remove the fascia from the buttons side cos i don't know how ,the buttons may just pull off but i wasn't going to force it .turn the bulb clockwise, and then with a small flat screwdriver on metal edge end of the bulb push right to release.its easy to replace the bulb . insert one end push the other end in the slot and turn counterclockwise.then refit screws and trim. I paid £4.99 for the bulb from a local hardware shop.
Toby, October 2009