In 1963 the author of “Traffic in Towns”, a book commissioned by the Ministry of Transport, cursed Oxford Street as a “travesty of conditions as they ought to be in a great capital city”. Things have only deteriorated since then. Shoppers breathe in the highest levels of nitrogen dioxide in Britain as they navigate a road that is among the capital’s most dangerous. Those who cram into Oxford Street’s crowded buses quickly realise it would have been faster to walk. They may soon have to. Sadiq Khan, London’s new mayor, has promised to pedestrianise Oxford Street by 2020 (it is already off-limits to private cars most of the time). The capital’s transport authority has previously warned that making big changes to the street is “neither deliverable nor desirable”. Built on a Roman road, it is one of London’s few east-west arteries. At peak times 250 buses an hour trundle along it, five times the number on Fifth Avenue in New York.