It has taken a lifetime for Roy Harper to win quite this much appreciation. This was a belated celebration for his 70th birthday, and the Festival Hall was packed with an enthusiastic audience who greeted his classic songs from the 70s with far greater respect than many of those who came to hear him in this same hall did back then. During one notorious show of that era he spent so much time chatting that most of the audience walked out. Since then, it has been impossible to predict how he will behave, but here – with help from famous friends, and despite problems with his voice – he did himself justice.

He looks today something like a crazed professor with receding long white hair and beard, but his acoustic guitar skills and acrobatic vocals are as keen as ever, as he demonstrated with a sturdy, rhythmic treatment of Highway Blues. Then he brought on an eight-piece string and brass ensemble, backing his playing with arrangements written by the late David Bedford. He nodded to traditional song and Dylan with North Country, and showed why he was so unique in the British folk scene, with his elaborate and epic 1971 song Me and My Woman, with his son Nick Harper, an impressive guitarist, joining in.

The second set was more patchy. His introductions were meandering, and his voice at times ragged; he stopped to retake the final verse of Commune and sounded uncertain during the exquisite When an Old Cricketer Leaves the Crease. But he returned to form when joined by new and old admirers. Joanna Newsom came on to duet on just one song, the gentle Another Day, while for the finale he was joined by Jimmy Page on acoustic guitar for a powerful, extended treatment of The Same Old Rock. Uneven, maybe, but a historic concert.