Have you calculated the floor space increase in percentage? Council looks at that if anything.
Any other extentions within the boundary over last .. say .. 20 years?
They take into account PC's comments, but do not follow them.
If your architect is good, he would ask a contact at the coucil, using the increase % figure and distance to boundary if an application was "likely" to be acceptable and succesful. Carefully take into account loss of "quality of lifestyle" your neighbour would suffer (if any) and any blocking of light to their windows. It "could" be argued to the council that a kitchen window and bathroom window do not contribute to loss of enjoyment of the neighbouring property. Pictures can help.