Agricultural activities are generally not affected by the scheduling of a site or monument. The farmer would have had to have wilfully damaged the monument to have committed a criminal act.
I had a quick butcher at the Wiltshire Sites and Monuments Record and couldn't find any mention of the site. Though it could obviously be known by another name and I don't have the local knowledge to spot it.
It could also be worth highlighting it to the county archaeologist.

http://history.wiltshire.gov.uk/smr/smr_search.php?parish_in=Warminster