I've been unable to find the nest which is somewhere in the roof. The wasps have been getting trapped in the loft area and eventually finding their way down into the living room following the flu but also getting into the bedrooms. What a nightmare!
I initially stood the insect killer on a box but it did not seem to be doing a lot of good, the ultra violet tube not being bright enough to attract the wasps in any great numbers despite the loft area being pretty dark. The answer was to hang the unit from the beam on the ridge of the roof and place a 100W lamp beneath. The lamp brightly illuminates the roof around the killer and the wasps go straight for it.
In addition I sprinkled ant killer powder on the surface that the 100W lamp is stood on. This takes care of any wasps which are attracted to the lamp and the bright surface beneath rather than the roof.
Taken together these two lines of counter attack are proving satisfyingly effective against the little devils.