The singer’s face is intense, flushed, contorted with emotion. It’s Saturday lunchtime in the centre of Kingston upon Thames, and she’s singing to a backing of bass-heavy pop standards while a small crowd listens. These days the street singers I walk past invariably strain, emote and grimace as they force their voices into acrobatic displays. Every song an exercise in purple-faced histrionics. In part it’s the fault of the TV talent shows: The Voice, Britain’s Got Talent, X F