Thanks for all your replies. Your stories are not surprising, which is depressing. Although my jaw did drop at the story of a woman feeding slices of brown bread to a pony in front of the owner!
For everyone asking about the geese, I did consider alpacas or Llamas as I would really enjoy watching ignorant twats getting spat at in the face but they are expensive and a lot of work, so they will be plan b if the geese are not effective. As angry as they can be, I find them quite lovely! We have been keeping them in until they are used to us so they will bond and follow us everywhere and we seem to be making progress. They run to the door of the shed now when we turn up, making these really sweet quibbling noises and are happy to stroll around us or sit at our feet now after they have eaten. Yesterday, they allowed us to stroke them while they ate! They are beautiful birds with pale blue eyes and I am delighted with them already. If we have to move to plan b, they will stay here as pets. I am nervous about letting them out but everyone I know who has them says that they bond very strongly. When out in the field with their charges, they stick close by as they like the safety of numbers and will scream blue murder if anyone comes near the female geese.
Part of me would love to get a bigger dog as a deterrent, even if it is just visual, but I do have a secret weapon in the form of a little toy breed whose yaps go through your brain like a spike. If I see people lingering on the path to their summer field, I let her out to scream abuse at them and put some ear plugs in. They soon move on and being "really fucking annoying" isn't an offence under the Dangerous Dog Act.
We also have an ongoing problem with a local cyclist who seems to find it enraging that I have the field gate to my driveway locked, and rather than follow the right of way, insists on throwing his bike over my gate and using my driveway and garden for access and for a nice sit down for lunch. He is incredibly abusive when being told to leave and we have had to barb wire the gate and fence posts to put him off as well as installing very tall driveway gates. He seems to be goading us into a fight. I haven't seen him for a while but it is hard to catch him all the time. I like the idea of getting more geese and letting them have the run of the yard, lying in wait for him the next time he tries this!
CCTV signs will also be going up as well as cameras as their winter field is out of sight of the house and I really worry when they go up there.
What gets me down is that I really don't want to be like this. I have no problem with right to roam, I use it myself when I ride and walk, but it only works if people are respectful. Too many seem to think it means, "go where you like and do what you want." :(