There doesn't seem any danger of that happening in the Royal Festival Hall. The audience roar delightedly when she arrives onstage, after the screening of a short film featuring her art performances, home movies of her and John Lennon and testimonials to both her artistry ("There's a reason the coolest guy in the world fell in love with her," offers one on the challenging effect her music has had on generations of listeners). "Whenever I started to sing in the studio," she protests in one interview, "people would go to the toilet." They'd find no relief there tonight: as part of her curation of the South Bank's Meltdown Festival, clips from her album Fly are being played in the gents, to pretty disconcerting effect.
Not that anyone here appears to be in any hurry to escape her singing: "I love you, Yoko!" cries a voice from the circle between songs. The octogenarian Ono's standing in the musical world has never been higher. You might suggest that's not saying much, given that she spent a significant proportion of her 80 years as pretty much the most reviled woman in rock, but then look at the names she has attracted to Meltdown Festival – Peaches, Savages, Deerhoof, Patti Smith, Thurston Moore and Kim Gordon of Sonic Youth – and furthermore, the names who lined up to perform on her 2007 album, also called Yes I'm A Witch: The Flaming Lips, Cat Power, Antony Hegarty, Spiritualized, Le Tigre.
These aren't Beatles obsessives looking for the glow of Lennon association: they clearly see Ono as a fearless musical forebear, determined to use the spotlight afforded her to expose a wide audience to the avant garde. They have a point. The loose-limbed, exploratory funk of 1971's Mind Train warrants comparison with the work of critically revered Krautrockers Can, and had it been by anyone other than the woman held to have broken up the Beatles, it would have got it years ago. It sounds fantastic tonight, scaled down from its original, mammoth length, decorated with Afrobeat-influenced trumpet.
Lennon seems to be directing proceedings, not always to his mother's liking: "You didn't have to stop right away. I was going to go on and on," she frowns as he draws Walking on Thin Ice – a song his father, steadfast in the belief that one day Ono's music would find an audience, thought would be her first number one – to a conclusion. Still, she correctly avers, they are "a hot band": they slip easily from scratchy post-punk to clangorous noise, from electronic drones to a riff that sounds not unlike a white-knuckled take on Led Zeppelin's Kashmir.
At the centre of it all, Ono cuts a hugely engaging figure. Most singers past a certain age suffer from a decline in their vocal abilities, but Ono sounds as hair-raising and potent as ever. She encourages the audience to flash torches handed out at the door and dances so wildly to the melee created by her band that at one point, the crowd breaks out in spontaneous applause. Somewhere in the hereafter, the coolest guy in the world is presumably allowing himself an I-told-you-so smile.