If the neighbour has planning permission he needs to stick with that. If he alters his plans then he must have your permission. I think this comes under the local Parish planning committee rather than BCO hence my comments. I accept the point though. The situation with the Durgo is a bit tricky because different people interpret the rules differently. My guide to Building regs states that it is OK to have a house with just a Durgo. (I have owned such a house). The proviso is that the branch (shared by other houses) has to have an open vent to allow sewer gas to escape. So a row of houses can have Durgos but there needs to be one open vent placed so the common branch is adequately vented. Now some people take this to mean that a house can only have a Durgo if it already has an open vent. I do not accept this interpretation but I have heard it a lot. It may be that you BCO has this same interpretation. You might usefully suggest to your neighbour that there is the possibility of some horsetrading here. Also try going over to the Hepworth site. Hepworth do a dry trap (the Hep2O I think) which does away with the need to have an open stack. They also have an information sheet to show BCOs that it really does conform with Building regs. This might solve the problem for both of you.