From the Historic England entry:
“Underground railway station. Built 1906 by the Underground Electric Railways Co of London Ltd (UERL) under Charles Tyson Yerkes, serving the Great Northern Piccadilly & Brompton Railway (GNP&BR), later the Piccadilly Line. Designed by Leslie Green.
Caledonian Road Station was originally part of the Great Northern Piccadilly & Brompton Railway (GNP&BR), one of three tube lines 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 he merged as the GNP&BR, and the BS&WR; 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.
INTERIOR: This was one of two Green stations (the other being Earl’s Court) where the lifts descended directly to platform level without an intermediate stair. The ticket hall was modernised in 1987 and has no original features apart from some sections of cornice. The straight stair down to the spiral stair retains original green wall tiling with a pomegranate frieze, and a timber handrail. The spiral stair also has original tiling in three contrasting tones of mauve, a bronze handrail and timber fire hydrant cabinet at the top. The platforms retains extensive tiling in the same mauve colour scheme, tiled signage, including the station name in dark-brown lettering on white panels and several original aedicular WAY OUT AND NO EXIT panels (others have been replicated), and sections of directional signage on trackside walls. There are also two metal roundels bearing the station name of c1910, very rare to survive in situ.
EXTERIOR: 2 storeys high. 5 arcaded bays with the entrance in the central bay and the former exit (now blocked) in the northernmost bay. Above the latter is the original EXIT sign in raised gilded letters; the sign above the entrance denoting the station name is a modern replica. The remaining bays are and always were occupied by shops; that to left (S) of entrance has a complete original shop front with decorative moulded corners to the transom lights and panelled doors; the other shop front is modern. Upper storey has altered timber Diocletian windows in keyed semi-circular arches with egg-and-dart decoration and cartouches between the springers of the arcade, and a modillion cornice.”