Disco 2 Interior lights staying on

After what seems to be a considerably long time without a murmur from my disco 2, well except when I needed a rear drop link at the last mot, the interior lights have just started playing up.
It rained like hell last night and when I got in the dico this morning everything seemed as normal, started first click and purred lovely, but the interior lights (front and rear) stayed on all the way into work.
I got out and tried opening and closing the doors and nothing, then suddenly they switched off so I locked up and went about my days work.
Coming home tonight, same thing again, the interior lights wouldn't switch off, so when I got home I had to manually switch them off.
I'm feeling lazy at the moment following surgery a few weeks back so can anyone direct me straight to the cause of this phenomenom so that I can fix it?

take the bulb out, and if it is water /damp let the car dry out

I went to have a look at things yesterday and all is as it should be. Lights working properly on door and ignition.
Clearly some water was getting into something and throwing the BCU some bad messages.
Anyway, i'll keep an eye on it.