People in general seem nervous of hornets. Maybe it's their large size and resemblance to wasps, that are also unpopular. In fact hornets are much less aggressive than wasps and are unlikely to sting if left alone.
They may be agitated by the use of cameras using flash and they dislike sudden movements and strong vibrations e.g. lawnmowing near their nest.

The hornet is Britain's largest social wasp and is becoming more common although it is still an endangered species. They are a very social species that live with a queen. The queen dominates the hive and is the only female to reproduce.
The queen emerges from hibernation in the spring and selects the nest site. It usually builds the nest in a hollow tree or in a cavity in a building. Sometimes in a chimney. It is constructed from chewed wood collected from trees and mixed with her saliva. A variety of trees can be used which is why the nest sometimes has a striped appearance. The inside of the nest contains many perfectly regular, papery-looking hexagonal cells into each of which the queen lays a single egg. These produce sterile worker hornets that care for the young, help with the nest building and protect the colony. A nest is only used once; hornets never reuse old nests.

As expected, a hornet's diet is mainly insects, typically grasshoppers, crickets, dragonflies, beetles, moths etc. They will predate wasps and bees. They also like tree sap and fruit. They take nectar from flowering plants and are useful pollinators. Eggs laid later in the year produce the females that become the future queens of new colonies. Other eggs produce the males that will mate with these females. Males are few and their only role is to fertiilise the females to produce future queens. These queens hibernate until the following spring and the cycle starts over again. The previous queen and the males die off.