The Underground was long a herald of modernity, from the steam trains puffing through the Metropolitan line in 1863 — the world’s first major underground railway — to the electrified deep Tube lines of the 1890s, to the sleekly designed stations of the 1930s. If that ethos disappeared in the post-war era and the nadir of the 1970s, perhaps it is returning now, with high-tech trains, refurbished stations and new lines once more.