NY expressed precisely :
In the kitchen we have a UV light electrocution device (similar to the
Insectocutor ones that butchers use) and a length of sticky flypaper. But the
flies seem to avoid both of these. The UV zapper is great for catching tiny
fruit flies, but larger bluebottle sized flies don't seem to be attracted to
it.

I had one of those UV units running for months a few years ago, it
never caught a single one. Most effective solution has been a mesh
screen across the often open back door, one of those that uses magnets
to keep itself closed. They normally provide Velcro to fix them round
the door frame, but that doesn't stay stuck for long. As it was so
effective, I simply made a frame to fix it from 20 x 20mm timber,
screwed to the door frame. We have had no more than two large flys in
the house so far this year, but a few of the really tiny ones.