From Historic England entry:
“Heritage Category: Listed Building, Grade: II
One of the most impressive surviving Leslie Green underground stations, including a largely intact faience facade retaining original tiled lettering.
Russell Square Station was originally part of the Great Northern Piccadilly & Brompton Railway (GNP&BR), one of three tube lines (see https://londonist.com/2016/09/a-guide-to-tube-pedantry) opened 1906-7 by the Underground Electric Railways Co of London Ltd (UERL). The City & South London Railway – the world’s first deep tube line – had opened in 1890 from the City to Stockwell, and although a flurry of proposals for further routes ensued, further progress was hampered by lack of capital until the Central London Railway (later the Central Line) opened in 1900. From 1901-02 the American transport entrepreneur, Charles Tyson Yerkes, acquired four dormant companies: the Charing Cross, Euston & Hampstead Railway; the Brompton & Piccadilly Circus Railway and the Great Northern & Strand Railway, which were merged as the GNP&BR, and the Baker Street & Waterloo Railway; the three were incorporated into the UERL in 1902. Yerkes died in 1905 before the tube lines were completed. The GNP&BR, or ‘Piccadilly Railway’ or ‘Tube’, opened on 15 December 1906, running from the Great Northern & City Line terminus at Finsbury Park to the District Railway station at Hammersmith, with 16 intermediate stations, increased to 19 in 1907, when a spur to Strand (Aldwych) was also added. In 1910 the three combined UERL tubes were formally merged as the London Electric Railway (LER) and the GNP&BR became the Piccadilly Line.
Leslie Green (1875-1908) was appointed Architect to the UERL in 1903 and designed 40 stations for the company in a distinctive Edwardian Baroque house style (a small number of stations, such as Regent’s Park, had no surface building). The stations were two storeys high, of steel-frame construction clad in brick and faced in ox-blood red faience produced by the Leeds Fireclay Co Ltd, with flat roofs to enable commercial development above. The elevations varied in their detailed treatment, but typically comprised a series of large arcaded bays, frequently incorporating shop units, with Diocletian windows to the upper storey, surmounted by a modillion cornice. Interiors followed a standardised plan adapted to the particular site, comprising a ground-floor ticket hall with lifts and a spiral stair down to corridors, and further stairs down to the platforms, which were usually parallel. The upper storey housed lift machinery. Ticket halls featured deep-green tiling with a stylised acanthus leaf or pomegranate frieze, and ticket windows in aedicular surrounds. Stairs, corridors and platforms were faced in glazed tiles with directional signage, produced by various tile manufacturers, each station with its unique colour scheme. Green suffered ill health and his contract with UERL terminated at the end of 1907. He died the following year at the age of 33.”
“In 1903 Stanley Heaps (1880–1962) became assistant to Leslie Green the architect for the Underground Electric Railways Company of London (UERL) and aided him in the design of the station buildings for the Baker Street & Waterloo Railway (now part of the Bakerloo line), the Charing Cross, Euston & Hampstead Railway (CCE&HR, now part of the Northern line) and the Great Northern, Piccadilly & Brompton Railway (part of the Piccadilly line); all distinctive with their striking red glazed terra cotta façades and semi-circular windows at first floor.
Following the early death of Green in 1908, Heaps became the UERL’s architect and produced designs for a number of new stations on the Bakerloo and Northern lines during the 1910s and early 1920s…
…After the Edgware extension stations, Frank Pick the UERL’s Assistant Managing Director, wanted a more modern style for the set of new stations on the extension of the City and South London Railway to Morden. Pick commissioned the designs of these from Charles Holden, who provided the designs for the majority of new Underground stations built in the 1930s. Heaps concentrated on the design of less noteworthy but nonetheless important depot buildings for trains and buses although he designed new stations at Osterley, Boston Manor and St. John’s Wood. Heaps remained Chief Architect for the UERL and its successor London Transport into the 1940s. He worked throughout that period with the Underground’s consultant architect, Charles Holden, on a number of stations including Hounslow West and Ealing Common.
During the Second War World Heaps served as Director of Construction at the Ministry of Aircraft Production.”