I am not the first owner (moved in last may). Houses are 1950's ex-council so my neighbour could have lived in the house from new and purchased from the council but I would have to ask her. I think her extension is about 20 years old and is not very well built. We have not entered into any specific covenants.
My neighbour accepts responsibility for the fence and admits that she had it erected but she is insisting that I fill in the gap opened up by the removal of my outbuilding. She has relied on my outbuilding to fill the gap (even though she could have continued her fence past my outbuilding to her own extension when she had it and the fence erected). The gap is in HER FENCE. It looks like I will have to swallow the expense of rendering HER WALL, but I don't see why I should have to also swallow the expense of extending HER FENCE which she should have, and could have erected it to it's fullest extent in the first place. Does her admission of responsibility of the fence change your reply in any way?