Like wasps, their nests are annual, though very much smaller. In autumn, queens are produced, which hibernate, and any surviving the winter try to start a new nest next year. The workers and males die.
You are quite lucky really -- they are scarce animals nowadays, and not found in all areas. They are not nearly as aggressive as wasps, and don't go for sugary things, beer and picnics in the same way. They are reluctant to sting, and only do it if squashed or really upset -- though the sting is worse than a wasp's. A friend of mine knocked a nest out of a rotten tree (also in Kent, in fact) -- he put it back, and wasn't stung.
Where is the nest entrance of yours? If it's well away from windows or doors, the best thing is probably to leave them be -- they'll only last a month or so more anyway. However, if they are getting in the house and you can't just shut that window, then pest control might be the answer.
I had a queen hornet in my office window this spring -- about the size of my thumb, looking for a nest site. I did consider letting her nest in the room, but on balance decided that was a little too close for comfort. Personally I'd not worry about a nest in my loft (but I've only had wasps so far...).
Hornets are predators of other insects, eating caterpillars, grubs, and anything they can overpower -- so they are a good thing in the garden, though more usually found in the woods.