Underground art is still fresh after 150 years It was during the Edwardian expansion that the exterior look of the London Tube station emerged. Forty stations were built in 1906-07 to a standard design, with ox-blood, glazed-brick exteriors on steel skeletons. Yerkes commissioned London and Shropshire companies to manufacture the famed, nine-inches-by-three, coloured tiles. He had a feel for colour, on a general, but not a rigid, scheme: usually with green tiles in the booking hall, up to shoulder height, and cream tiles above. There was great variety across the network: Caledonian Road station had tiles in three shades of plum; Hyde Park Corner was brown with pale yellow details; Kennington Road gold and dark blue. There were also elements of the Art Nouveau, twirly-whirly lines of the Paris Métro - particularly in wrought-iron entrance gates to stations such as Regent's Park. Even the lift shaft ventilation grilles were decorated with playful Art Nouveau detail - sinuous iron leaves and twisting railings - worthy of Charles Rennie Mackintosh. Architectural innovation continued into the 1920s and 1930s. Charles Holden's 1926 design for Underground headquarters - over St James's Park station - produced Britain's first great Manhattanesque skyscraper. Jacob Epstein's sculptures of Night and Day for the building were considered so outrageous that, in an intentionally absurd compromise, Epstein cut an inch off the penis of the naked boy in Day. Holden's 1930s modernist stations on the Piccadilly Line were equally revolutionary. Elsewhere in Britain, we never really got into Art Nouveau and Art Deco the way they did on the Continent - our Art Deco flat roofs leaked in the rain, which stained the white concrete walls and leaked through the curving windows. The same went for baroque 200 years earlier - in our cool, northern way, we've always recoiled from anything that smacks too much of pretension or southern, hot-blooded Catholicism. But the Tube was given free rein by a series of broad-minded designers and administrators. The best known is Frank Pick, commercial manager in 1912, and the first chief executive of London Transport by 1933. Pick established the distinctive Tube poster, encouraging artists and printers to apply an Arts and Crafts look to modern technology - a combination dubbed medieval modernism. Pick commissioned Edward Johnston, an expert calligrapher, to design the Tube font, now known as Underground Sans, in 1913. Johnston also designed the Underground bullseye, or roundel, sign in 1925. Underground Sans looks simple, but Johnston's demands were exacting: his O is a perfect circle, his capital M a square with the diagonal strokes meeting exactly in the middle of the letter. Pick was also a ruthless commercial operator. He ensured the Johnston letterface was copyrighted to the Underground Group; another reason why the font signals "Tube" loudly. The same combination of original design and commercial protection applied to Harry Beck's 1931 Tube map - dreamt up in his spare time and offered to the Underground's publicity department. His innovation, like all great ideas, seems obvious: to abandon geographical accuracy for the sake of a simple diagram. Still, the Underground management didn't think much of it: they paid him only 10 guineas, and sat on the map for two years, before finally releasing it, to popular acclaim. The delay was a rare aesthetic lapse by the Tube authorities. They didn't just build the first underground railway; they built the best-designed one. Harry Mount's 'How England Made the English" is published by Viking