Reversing Light 12 Volts but not illuminating

[The Law]

HI I have 2004 Avensis, I noticed that the reversing light was not working so first checked the bulb in another socket and the bulb worked fine. I then put a multi meter across the reversing socket whilst reverse was selected and it read 12 V. I then put the car in Neutral and it showed 0 V so the reversing switch I guess is working fine. I cleaned up the socket to ensure a good connection onto the bulb and still not working. It has me scratching my head what the fault could be any advice would be much appreciated.