Following the Grouping of the majority of Britain's railways in 1923, the "Big Four" all found themselves the owners and operators of most major ports, docks and harbours - along with, in the case of three of them, being significant ferry operators in their own right. The 'odd one out' with regards to the latter was the Great Western Railway.
However, the GWR did have some significant port and dock facilities, most notably in South Wales due to the export of the prized coal mined in that region, as well as much smaller facilities such as Brentford Docks in west London along with Chelsea Dock. This is the July 1931 edition of the Docks of GWR and that appears in a remarkably small format; the company also issued a "Great Western Ports Annual", a larger and more expansive format. This contains no adverts and is simply a resume of the company's shipping facilities with a section of plans and maps of the various ports and docks. The GWR's Chief Docks Manager's Department was based in the substantial building overlooking Cardiff Docks.
Given the format and the tight binding the plans, on very thin paper, are almost impossible to open without damage. I have managed a scan of this; the plan of Brentford Dock in Middlesex, west London. The Dock was a transhipment port for goods between the GWR, who ran a branch line down to the Dock, the canal and the River Thames as well as serving local industry in this part of Middlesex. Passing to the British Transport Commission/British Railways in 1948 the Docks were a working port until 1964 and in later years ownership passed to the Greater London Council under whose stewardship it became a Marina along with redevelopment for housing.
