OK, a strange one...
Open then close the boot, switch the headlights on, and the drivers side tail light fails to illuminate. Give the light lens a thump and it comes on. Thereafter it works fine if the lights are switched on then off etc.
I've repeated the above several times and it never fails to follow this pattern so I'm reasonably convinced the the opening and closing the boot triggers the fault. However, I've no idea where to start looking. It seems ridiculous that a fault that occurs so reliably can be fixed by a light knock on the light.
Grateful for any advice.