It seems that the 'damage' is under investigation, one of the henges has disappeared? due to tree planting and re-seeding, it will be a great pity as Priddy Henges are unique..

Archeologists are assessing damage to a 4,000-year-old prehistoric site on the Mendip Hills.

English Heritage experts have been investigating claims that one of the four Priddy Circles, which are Scheduled Ancient Monuments, has been obliterated.

http://www.thisissomerset.co.uk/Fears-Priddy-Circles-obliterated/story-12782536-detail/story.html