In reply to Andy Say:
Vixen Tor is well inside the Dartmoor NP Boundary. It is not, at present, subject to Open Access under CRoW.
All National Park boundaries are simply designated for planning purposes not access, and most of the land area of any NP is privately owned. On Dartmoor, the Duchy of Cornwall owns a huge swathe of the open moor, other areas are owned by the various Commoners and much of the marginal land (newtakes or intakes) is owned by individual farmers and landowners.