Shuffling into a railway arch by one of London’s busiest road intersections is a queue of hungry people. But this is no Vauxhall soup kitchen. Instead the crowd is an eclectic mix. There is a barrister, loudly discussing his latest case, a few people in bike gear, a group who have just emerged from the Tea House Theatre and a young man – my son in fact – who is on a quest to find the best burger in town.The joint is Dirty Burger, London’s hippest new outlet and one among dozens of new “gourmet” burger chains. Burgers are the new risotto, someone quipped. Interesting thought, given the acceptance that the fast-food-guzzling social slice is supposed to be low-income and poorly educated – and destined for obesity and our hospitals’ cardio-vascu