A friend had this but on a much larger scale, twenty years ago. They took a 30ft by 300ft strip. Said possession was 9/10th of the law and he couldn't do anything about it. He got onto the OS and bought some old aerial photographs and maps to show where the boundary had always been. Got some old guys from the village to say where the boundary lined up. The crims made threats that my friend's kids would be attacked. In the end an injunction sorted it out. They had to remove their new fence and put everything back to how it was. They did it hours before the deadline. It was very nasty.
Bill