Access to maintain drainage pipes

I have recently moved into a new house in a villa estate in Sai Kung, the house is detached but one side is adjoining my neigbours plot on the east boundary. I have sewage and water pipes on this side of the house. My neigbour has now decided to build near my wall were my pipes are. I am worried that he will block my access to maintain or replace any pipes or prevent access to paint the wall. My question is does anyone know if there is a common law of right of access for example, 3 foot from boundry line or property line to allow any maintainance? Secondly is there any law that states waste water pipes should be underground or can they be at ground level for better maintainance? MY neigbour intends to block access and has stated that we would need to seek his permission to gain access. However he intends to build a structure which would not be easy to remove to gain accesss? Would I need to pay for the removal of such structure every time I need access? Any advice is much appriciated.

Well he can't really give us a straight answer, but it will be some sort of wall or fence around his garden, which we are quite happy for him to do because it will improve the area, but he wants to put it right up agains our existing wall meaning we'd need to remove each time we need access. Sadly we can't go to the SKDLD as we bought the house with an existing stucture that could be illegal, as do most houses in this area, so we're trying to be reasonable but our neighbour is being very unreasonable. The deeds do show that our property ends at our wall and his begins, but our water meter and air-cons are also on that wall so surely must the right to get access. The last thing we want is to have a bad relationship with our neighbour.