The bulb has definitely gone this time.
So, following the guidance here, I tried to replace said bulb.
Only to find that the bloody lamp assembly wouldn't shift for love nor money.
Ended up removing the interior plastic.
Turns out that, for me - 2006 model - the way to do it is to pull the lens assembly on the left hand side THEN push on the right hand side, moving the whole thing towards the left.
This compresses the spring clip and allows the hooked retainer to disengage from the body.
To refit, make sure the hooked bit is in place before pushing the assembly firmly into place on the left side.
Oh, and once the assembly is unclipped, it's quite a tight fit under that plastic guard so needs a bit of jiggling to free it.
Luckily, I had a spare bulb - it's one of those tiny 5w capless bulbs as per post
#5 ^^^