Out of interest how do the police find out who owns a bit of grassland? I assume it's out of the way if you suspected green belt, just wondering at the amount of effort they had to go to not only to work out who owns it but to get a phone number (was it mobile?) to tell you something that they can't be arsed to do anything about themselves. Considering my last few attempts to report actual crimes I'm amazed it wasn't completely ignored.
Is the land obviously a specific parcel, boundaries obvious etc. so it was easy to tell it was your land that was allegedly being used? Is it near any houses?