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so just to be clear
In 1993 it's likely the builder has sold my property including the boundary fence to the original buyer. A few years later 1999/2000
a different builder has sold the neibours on the other side of the fence their property and the fence.
meaning both properties have been registered with deeds at different times that oblige the owners to maintain the same fence.
How can the other builder sell something that is not his to sell?
Not sure I understand what you are saying, My deeds refer to the 'T' marks on the plan in relation to maintaining the fence in question.