The sections of the diagram of British Rail's April 1965 "Greater London Network Map" issued here as a folder and that was also produced as a Quad Royal poster map. In the latter format the diagram carries the name of the designer, D.J. Lowten.
The diagram follows, in some ways, the Beck diagram of London Transport in depicting the complex suburban system of British Rail both north and south of the Thames. This is a relatively early outing for the new British Rail corporate identity.
I've had to scan this in two sections; this shows the bulk of the City of London along with the network running out north and east into Essex and, south of the River Thames, into Kent and south to Sussex.