They weren't done under the 1979 Act, and couldn't have been, but under a special Stonehenge-related order sponsored by EH - The Stonehenge Regulations 1997 - which also make you liable for prosecution if you even step onto the site without their permission or enter it from a non-authorised direction or take your dog onto the site (take note Moss... )http://www.opsi.gov.uk/SI/si1997/19972038.htm

Seems a bit over the top to me. Still, they seem a good set of lads and had the last laugh - one of them was allowed to carry his club in court and "had insisted on being addressed throughout the proceedings as "Mrs Hodge" having changed his name by deed-poll to Margaret Hodge, the former Children's Minister."
http://www.thisiswiltshire.co.uk/news/headlines/display.var.1755708.0.flintstones_fined_for_stonehenge_stunt.php