The footpath belongs to the Highway Authority (A strip on land above and a block of air above it).
You can walk to the end of the path and thats it. It does not give you a right to access the monument. So if there is a fence at the end of the path, you can only look over it at the site.
Is the site SMR ? I expect then your still not allowed access without permission.
and
If the land has intrefered with it (fence touching it) thats a 20,000 fine. As if anybody going to get done for it Haaa.
Ike