Over the last couple of weeks my bulb monitoring warning light has been flashing intermittently yet both the bulbs are working fine. When it flashes I just tap one or other of the brakes and the light goes off. 
I suspect it could be the bulb monitoring unit itself but can't find any info on it in my clymer manual....where to hell is it? and what does it look like?
Am I even barking up the right tree?

BMU you find in the middle of the LHS in the relay box.
Also check that the bulbs have good ground connection.

had the same issue a couple of times

the tail light globe was just about on its last legs and a slight bit of corrosion in the bulb holder socket  as I hit a bump it would come on mysteriously .

changed the globe and cleaned up the corrosion and added some deoxit ....all good since