New neighbours moved in next door and immediately put up a planning notice. We're a terraced house in a block of four, and the new neighbours are at the end-of-terrace. They are planning to more than double the size of the existing house, with a mixture of one and two-story flat-roofed extension. Our back garden is narrow and north-facing. They plan to build their single storey extension right up to the boundary. This will cut off about a third of the sky visible from our back window and make the back garden something of a tunnel. The extension will be a flat roofed kitchen with skylights that will be just a few feet below our back bedroom window (on their side of the boundary obviously). They also plan to build a new seven foot dividing wall along the whole back boundary. I don't want to kick up a fuss unnecessarily. The new building will certainly be something of an imposition on us, but as I understand it the effect on our light is not valid grounds for an objection. Can we/should we pursue this. What would be valid grounds? Is there somewhere I can go read about all this stuff? Even if we don't object I'd like to understand issues such as overhangs and gutters etc. The cutoff date is not too far away, with Christmas intervening.