Administration Building within the 1935 Building, Royal Mail Sorting Office

The Administration Building, part of the 1935 Royal Mail Sorting Office, is a two-storey structure faced in limestone ashlar. It features a large plain hipped roof covered with slate tiles, while the roofs of the wings are concealed behind parapets, and the pediment roof is clad in lead.

This building is single-depth and is separated from the Sorting Hall by an internal partition wall located at the valley between the two roofs. The exterior consists of nine bays, with three central projecting bays flanked by two recessed bays and a single-bay wing on each end. The outer bays are smaller wings, while the main block has a three-bay centerpiece. The ground floor has taller sixteen-over-twelve sash windows on either side of twenty-over-fifteen windows in the center, three of which feature round heads. The second floor has eight-over-eight sash windows. The central three bays are framed by giant pilasters in the Roman Doric order, supporting a pediment that displays the Royal Arms of George V and the date 1935. The west side of the building connects to the sorting hall, where only the second floor is visible, featuring metal casement windows.

Inside, the Administration Building retains much of its original layout, although some later partitions have been added. It includes four-panel doors with over-door lights above, although many other doors have been renewed or replaced. There are stairwells with timber handrails at both ends of the building, and all rooms have false ceilings.