A right of way can be extinguished by non-use or abandonment after 30 years. Public Highway can never be extinguished except by an unopposed Magistrates Order -a 'stopping-up order'.
There is a lot of caselaw, Appeal Court, stuff on this subject. I had it all thrown at me when I bought some access land and was told I couldn't use it all because part of it had been abandoned. It would have to go to court for a ruling and may then go to Appeal. Expect a bill of at least £30K for the loser, £10K for the 'winner'.