I was studying a zoomed in version of the LIDAR for the avebury area I posted yesterday and spotted this:
https://houseprices.io/lab/lidar/map?ref=SU1183869019
https://www.google.co.uk/maps/@51.420065,-1.8311421,387m/data=!3m1!1e3
Checked the Wiltshire HER and it doesn't seem to have been noted. I thought it might be a crop circle as there is one visible on the LIDAR to the North East of Avebury, but there it is on a google maps satellite image as well.