I believe the actual ILS system installed in the late nineties is CAT 3 Capable. However, even fitting the lights to only the 12 end, (you couldn't use 30 anyway due to the cliff which is why BRS hasn't got it on 09) would be very expensive. Although you might be able to get the whole job done cut price just now ! Not sure whether there might be a problem with the locating of the BA hangar as well for full CAT 3 but Cat 2 would be sufficient in all but the very worst weather (probably one day a year).