I bought a property in june 2013 which needed extensive modernisation internally and externally. Part of this refurbishment was a reroof to the main roof, extension roof and replacement of the flat garage roof. I opted to have a mono pitch roof to go onto the garage which wraps round the back of the house incorporating the extension reroof. My builder used the existing garage wall to build upon and this was built inside the boundary line. My neighbour had built their single storey extension up to the boundary line. My roofer has situated the guttering so it sits over my neighbours flat roof part way along the length of the garage. (I didn't know the builder was doing this until it was finished. My neighbour spoke to me about 4 months ago about it saying she didn't"like it" and cited difficulties if she had to have roofing work undertaken. I offered to unclip the guttering if shr needed access to undertake such work. I also offered to remove the guttering and not replace it. Now she has written to me stating that neither option is acceptable to her quoting"trespass of water" if I remove the guttering. The work has been passed by building control, and they have advised the only alternative is "box guttering" which they state is costly and prone to leaking (so I still risk trespass of water). I am unsure how yo proceed with this now because if I have to remove the garage roof it will have implications for the extension roof as well. Does anyone have any suggestions? Many thanks