ANYWAY, you don't have to remove the white plastic part as I'd remembered. Just remove the front of the switch to access the bulb. There are two tabs, one top and bottom which can be pressed with a small screwdriver once the switch is out. Alternatively and depending on how worn the switch is, the front may come off just by pulling. In which case the rear of the switch could be left in the binnacle.
The bulb itself appears to be a grain of wheat style bulb, and I've not (yet!) attempted to pull it out. You can see it, and one of its leads, in the photo:

