Whose were those feet in ancient time that walked upon England’s mountains green? That William Blake assumed his readers were on his same wavelength is one of the things, according to John Higgs, ‘that makes his writing a glorious puzzle’. Equally puzzling, argues Higgs, is that the cockney visionary, unsung in his lifetime and buried in a pauper’s grave, has now been absorbed thoroughly into mainstream culture without our having the faintest idea of what he was on about.