The biggest challenge for an older artist with a lengthy career is to stay relevant and keep their audience interested. Some manage this with ease – Nick Cave has rarely put a foot wrong since the beginning of the 80s, for example – but most, including ‘godfather of punk’ Iggy Pop (on the scene a decade or so longer than Cave), will inevitably start to fly slightly under the radar after a while. In his early days he always worked best with strong collaborator, be it the rest of the original Stooges, James Williamson in their later incarnation – though none of these were quite able…