Inheritance property on someone else's land

[easdale2013_gmail_com]

Hi, I inherited a house with some land. The problem is there was an agreement between my mother and her neighbour regarding the building of a shed. My mother was to pay for the shed but it was to put on the neighbours land. Both were allowed to use the shed as their own. The neighbour now insists I remove the shed(at my expense). The shed has been there for perhaps more than 10 years. I.e neighbour is council tenant. I just received a letter from them 'asking' me to remove it. Am I protected with the 4 or 10 year rule? Does that rule only apply to my mother. 

Thanks