It’s been nearly six decades since Ralph McTell, the singer-songwriter from South London, was shot into enduring superstardom after the release of Streets of London.  The poignant vignette, originally conceived as “Streets of Paris”, sold upwards of 90,000 copies a day at its peak, earned McTell an Ivor Novello, and became a global anthem covered by some 200 artists to date. Alas, when a song comes to define a singer, the plush, professional blessing can tend towards a personal curse.  How does he feel about it today?  “There was a time where I thought that if you peak at 22,…