In April 1969, The Beatles released a song that was supposed to prefigure their return to the rock and roll roots that first took them from Liverpool to London via Hamburg and on their way to global fame. ‘Get Back’ turned out to be the only song released from the project, apart from its B-side ‘Don’t Let Me Down’, until two final singles were released alongside the album Let It Be a year later, without Paul McCartney’s permission. The Beatles d…