For any right or easement to exist there has to be a dominant tenement and a servient tenement. The dominant tenement is the land enjoying the benefit of the right and the servient land is the land subject to the right.
It is worth noting that the owner of the dominant tenement with the right cannot “extend” the dominant tenement to encompass other land. So if the owner of the right owns Goodacre with the right and subsequently acquires Betteracre, the right does not pass to Betteracre too. The right attaches to the land not its owner. Sometimes there can be confusion where Betteracre leads off Goodacre and only Goodacre actually enjoys rights of access over a track on the serivent land. The owner of Betteracre and Goodacre may be entitled to drive his tractor along the track to plough Goodacre but cannot (lawfully at least) take his tractor along that same track to cross Goodacre to reach Betteracre to plough the latter.
Any right or easement will merge and become of no further effect if the dominant tenement and the servient tenement come into the same ownership. When the ownership is split again later the right has to be recreated by fresh grant. This is as relevant to registered land as to unregistered land, and to a mixture of the two. There may, for example, be two different land registry titles for the dominant and the servient land respectively but the same ownership will lead to merger, even if the entries relating to the right remain on the title registers and a later sale or lease of one or the other will make no difference if no more is done. This point can sometimes be missed!
A right of way, once obtained, is difficult to lose by lack of its exercise (even if never exercised) or very long disuse. The servient owner should beware and take great care if tempted to block off the right, or maintain locked barriers without the supply of a key to the dominant owner.
Every case depends on its facts but a right of way on foot is most unlikely to imply a right of way with vehicles. Similarly intensification of use may not be lawful. Therefore if the use of the dominant tenement changes, for example a field becomes the site of one or more dwellings, the right of way may not necessarily be lawfully available for use by the owners of the dwellings.