Tom Jones is standing by the drum riser, his back to the audience. Pretty but inconsequential melodies trickle from a guitar. Something isn't right about this mid-set lull. After an animated chat with his drummer and a shadowy figure from the wings, Jones returns to the microphone to sing (I Want To) Come Home, a latterday Paul McCartney number, his voice confessing vulnerability. Then comes the real admission. He has forgotten the lyrics, and needs a prompt.

Until that moment, it would have been easy to read Jones's mild bemusement at being included in this year's Blues Fest, and the seam of humility in his demeanour, as a calculated scuff to a professionalism so focused it feels workmanlike. Two songs later, when he steps on to the surer ground of his mid-1960s hit Green, Green Grass of Home, you understand why he might feel grateful. For two decades, his best was behind him. With his 2010 album Praise and Blame and this year's Spirit in the Room, he has reintroduced risk to his career and the idea that his best might be yet to come.

With those albums dominating the set, Jones can stretch his personality, shifting from devil-wary preacher to hell-bound sinner, glimpsing heaven through the eyes of the contrite and trampling earth in the boots of ruffians. Not all of it works: St James Infirmary Blues is too bedazzled by its own roistering, and he's too much the contented entertainer for the furious gospel of Lord Help. But in his less polite moments, he seems transformed. Burning Hell genuinely blazes, Just Dropped In is silkily louche, while Tower of Song becomes his personal My Way, confession and celebration at once. From this new vantage point, answering the inevitable calls for Delilah is a lot more fun.