Hi Richard, There is another thread running on this called "strangest places for a nest" I think.
Anyway we have blue tits feeding young in a street light, the light is larger than the house and stopped working 4 weeks ago, probably not a coincidence.
Its in full sun all day but has a pale plastic casing so hopefully they will not roast in there, the next challenge will be fledging, its either fly or fall
I hope someone does not come to fix it either, if its opened up the whole nest will fall i think.
Anyway we will be observing, and hopefully see a good outcome!