The ANO does restrict vehicular and person access to "aerodromes". I am not sure whether "aerodrome" means a one that is licensed or would include a private farmers strip. If there is a right of way across any aerodrome, then pedestrians have a right to be there.
But here is a question - how does the right to roam affect this scenario? If Long Marston is un licensed, does the general public have a right to roam, even on taxiways/runways?
Indeed anyone who operates to a private or unsecured site has to be cautious as to who might be lurking......
Accident or otherwise it is not a good day for aviation, hunting or antis.