It has long been the law that you cannot lose the benefit of an easement simply by failing to exercise it for a long period. In other words, non-use for however long a period is not enough by itself to amount to abandonment of a right of way.
This has recently been confirmed by the Court of Appeal in Dwyer v Westminster City Council in which the council successfully sought to reinstate a right of way over a passageway that had been disused and blocked off since the 1960s.
To constitute abandonment any non-use must also be accompanied by an intention on the part of the beneficiary of the easement never to re-assert the right or to attempt to transmit it to anyone (Tehidy Minerals v Norman (1971)).
Note that the Law Commission has proposed that the law of abandonment be changed. It has proposed that if an easement has not been used for a continuous period of 20 years there should be a rebuttable presumption that it has been abandoned.