Ask an Property Solicitor. Get an Answer ASAP.
I am afraid that as the Land is not registered at the Land Registry, there will be no public record as to who owns it. So, it comes down to good old fashioned detective work and all you can do is to ask the neighbouring owners as to whether or not they know the name of the owner.
I am sorry I can not give you better news, but I hope I have answered your question from a legal perspective.