Oh that it were that simple!
Public rights of way have their origins in Common laws which have been much modified over the past 100 years or so by statute. This has lead to considerable complexity in the law, although recent statutory developments have done much to bring the law in line with modern needs. It is still a complex area and it may be found more edifying to find out how to prevent the creation of a public right of way than its creation!
Chapter 3 of Countryside Law, Garner & Jones, Shaw & Sons, 1997 ISBN ) 7219 1062 9 is a good starting point, whichever direction you may wish to travel.
Highways Act, 1980, Schedule 6, thereof, is not commonly used to create PROW. Its use is rare outside the creation of the now established, long distance footpaths.
In this situation (the thread) I would expect to find a letter,notice or memo of rebuttal (of presumption of dedication) lodged with the Council (County &/or Parish).
CADW, if involved, will be interested in this area for the creation or easement of site access.
Is all CADW property inalienable or do they also hold alienable titles?