I have hornets( & wasps) nest under the roof tiles every year, they occasionally come into the house when the windows are open, I've never had any problems & find them less aggresive than wasps. In the autumn I leave a large container full of sugar & jam which keeps away from us.
I remember once in the corsican mountains, I flipped over a large flat stone & there all bundled together was a mass of writhing hornets, it took a second or so to realise what they were, as I had never seen black ones before, & I must have run 100 metres in less than 5 seconds, seeing that they hadn't come after me, I slowly walked back to take a better look ( shaking like a leaf) & maybe try & put back the stone, as I approached they started to 'agitate' & spread out so I thought it would be a good idea to clear off. I think it was the cool temperature (15° c) that kept them nailed to the floor.
If there is a nest that you have to pass regulaly, I think it might be wiser to slap a demolition order on it now rather than later, on a cool morning just take off the nest & put it elsewere, then they should start to build another hopefully somewhere else. I believe they make new nests every year & don't use the old ones, but I'm not an expert.
