I'm not familiar with building practices in the UK, but based on your image I am guessing it's similar to the US. Generally, wood studs are pre-cut to a certain length - when combined with the bottom plate and two top plates, and then drywall installed, the desired 8' (or 9' or 10') ceiling height is achieved. Unless essential to whatever the wall finish is, typically the studs (verticals) are not placed symmetrically, and are spaced 16" or 24" on center from one end or the other, and extra framing for doors and windows added as needed (the standard 16" or 24" spacing is useful for determining location of the framing when the drywall is installed and the framing is hidden from view). The horizontal blocking would only be installed if needed for installing millwork (cabinets) or such. It's not clear what will happen with the chimney breast - will it be built in front of the wall? What's it made out of? Is the fireplace a pre-fab insert, or solid masonry?
wall-framing-diagram.jpg
