This is quite a common occurrence, the applicant has added a balcony to the back of their house, which is specifically excluded from Permitted Development Rights, and always requires planning permission. There is a real privacy problem with balconies, whereby people can openly peer into neighbours' gardens, and so on the majority of applications for new houses and extensions with balconies, the planners take care to ensure that this issue is eliminated with careful design and quite often the addition of frosted glass side screens.
This application is a balcony on a terraced house, the design includes timber balustrades and screens on each side, but the planners have taken a view that it intrudes on the privacy of the neighbours. There is no real way around this, if the applicant goes to appeal the inspector is likely to assess the real impact on the privacy of the neighbours in their decision, which we suspect is likely to be unsuccessful!