Hello. I am a solicitor with over 15 years experience. I will try to help you with this.
The key concept here is adverse possession, which means that if you have used your neighbour’s land openly without permission, as if of right you may have been in adverse possession of their land. The old law on this was that if you did have adverse possession of the land for an uninterrupted period of 12 years you might be able to claim that the land is yours.
A new law was passed regarding adverse possession of registered land which meant that for claims for adverse possession arising after 2002 it was much harder to acquire through adverse possession rights to land.
The old law was retained for those who claim to have acquired rights to land by adverse possession before October 2003. On the dates you give you could well be in the situation where have acquired the land through adverse possession.
Do you accept that the neighbour is right in his assertion that his father made an error? Were you in occupation when the current boundary was established?
I was not in possession when the fence was errected but have been
using the land since 2001 when me and my wife purchased the property