Photo by Carl Court/Getty Images Stevenage, a Hertfordshire town 30-odd miles out from London, is crumbling under the weight of its symbolism. Literally. The leader of the council says it was about 15 years ago when all the Fifties concrete here passed its best-before date. As Britain’s first New Town, slotting Blitz-dizzy Londoners into its grid of council terraces and pedestrianised plazas from 1951, this was ground zero for the utopian ideals of a postwar nation. Now, its concrete looks a little soggy and sad. The classic layout of the original estates, with houses facing out into green spaces and quiet walkways, and cars hidden behind the backdoors, has meant many residents simply stopped using their front doors and mowing their front lawns. A place designed to provide everything you need in life within walking or cycling distance (it’s home to Britain’s first bike lanes) now functions largely as a commuter town.…