Hi all, many thanks for your responses. They have helped me massively.
I have learned I also need to be more transparent about how I feel and when talking / responding that I need to not talk about any emotions, but the detail.
My position is this - I have concerns about the plan. I also cannot allow this plan to pass by not being properly scrutinised by those with expertise and authority - therefore I have to voice my concerns. If the plan was submitted in a way the council approved it, then I would respect the decisions.
I am also going to be honest with the neighbour and the architect about this position I am taking and hope they understand i'm not trying to be a constant thawn in there side but I could work with them in the future on revised plans. However the pressure on me to be the sole decider to a decision that can have a lasting impact isn't something I can do, so I had to voice my concerns honestly.