Assuming generalities from a few observations is risky, I think there is a lot of truth in Ninthace's post, however I would not like to give carte blanche to conservationist without investigating some of the counter situations. One springs to mind;
There is a gorge on the River Theme just west of Ludlow. So beautiful by repute that it was part of a leisure walk landscaped by one of the Georgian or Victorian landowners, however the land has little agricultural value, so it was off loaded to some nature organization. There are non highway bridges at either end, one a right of way the other not, but strong circumstantial evidence that it is a lost public way.
The warden upto 10 years ago arranged bi-yearly visits through the gorge and by all reports these were more of a personal ego trip for himself rather than a true allowance of access. I know a person who lived in the neighbourhood of this person, who promoted himself as a great conservationist, yet his local reputation as a control freak was well established. The legacy from the occupation is no permissive way along this beauty spot, which could highlight the second bridge as a strong contender for further access. If that was so it would show on even a cursory glance at an Explorer map a route that joins Ludlow to a station on the central Wales line.
This would be a significant step in creating an A1 route across the South of Shropshire, a county that only has a meandering circular route as it main contribution to the countries access and manages to block the East to West approach to the Welsh border from the densely populated Midlands on South, Mid and North bands.
Sorry but I would like to see more recognition that withholding keys parts of our countryside and infrastructure that can benefit access needs to be understood before we risk making a class of occupier more reactionary than the hereditary landowners, who still need to come clean about the political crime they perpetrated.