Erection of a hip to gable end roof extension; lowering the ridge height of the main roof and erection of an additional floor at roof level; raising of the front and rear parapet walls; alterations to the first floor roof of back addition to include the installation of new rooflights; alterations to the front fenestration to include the installation of new windows at first floor level, new windows and doors at ground floor level to replace the existing doors and windows; alterations to the rear fenestration to include installation of new windows to replace the existing windows at ground floor level; removal of existing windows at first floor level to the rear elevation; lowering of internal floor level and change of use from office (Class B1) into residential (Class C3) in connection with the conversion into 2 x 2 bedroom self-contained flats.