She is in great shape, although - as she sings in broad daylight for 50,000 souls in aid of the Prince's Trust - the tension that invariably accompanies Diana Ross is present too. Much to her chagrin, her microphone stops working after Love Hangover, possibly in protest at how croakily the song had been sung.

She twice interrupts My World Is Empty Without You to demand "more bass" as if she were being backed by Black Uhuru rather than a band that later, on a galumphing Upside Down, proves itself to be less Chic and more Chicory Tip.

Then, to the bamboozlement of band and audience alike, she repeats sections of I'm Still Waiting in the manner of a particularly exasperated schoolteacher, ordering the crowd to sing along "but this time with feeling".

Despite having 40 years of distinctly singable hits to select from, Ross's finale was a dreadful assault upon Gloria Gaynor's karaoke staple I Will Survive. Not only does she have the body of a much younger woman, Ross is hijacking their songs too.

However, in her allotted hour Ross manages five complete, lightning-quick, costume changes, earrings and all. And, despite being presented by the empress of the unnervingly fixed grin, these songs exude joy. The electric drum roll of Chain Reaction is still a bouncy delight; Theme From Mahogany (Do You Know Where You're Going To?) remains a classic know-thyself affair and, if there must be syrupy ballads, they might as well be Endless Love.

In order to leave more time for the crucifixion of I Will Survive, what she now christens "the super-dooper Supremes sound" is tossed off in a spirited medley. Authentically returning us to the 1960s, she does that dance to Stop! In the Name of Love. It would have been a more accurate reflection of the times had she pushed over a backing singer. Scary, but perversely compulsive.