Simon Price on Jane Birkin: Jane reignites her flame for Serge Gainsbourg

The inimitable Monsieur Gainsbourg, 'France's finest poet', has been dead 20 years. But his ex-lover and muse sings on at London's Cadogan Hall

Sixties siren: If Birkin’s cheeks were any higher they’d be in her eyebrows

When Serge Gainsbourg photographed Jane Birkin nude for Lui magazine, he described her in its pages as "my little hermaphrodite". At 66, Birkin is ever the androgyne. It isn't just that her current tour involves singing Gainsbourg's none-more-male oeuvre (without altering the gender of his lyrics), notably including "Ballade de Johnny Jane", taken from a film in which, she reminds us, she effectively "played a boy". Slouching around in white shirt, black slacks and martial arts slippers, it's almost as if she's channelling Serge.

Gainsbourg, who died in 1991, was, Birkin tells an overwhelmingly Francophone auditorium, "France's finest poet, and the one they miss the most". She, meanwhile, was his muse, the Faithfull to his Jagger. When, aged 21, she met Gainsbourg on the set of Slogan, she'd already been a teenage bride to John Barry and the first full-frontal nude shown in British cinemas (in Antonioni's Blow-Up). At first, Serge feigned disinterest, but before long they were shacked up in Oscar Wilde's old Parisian hotel room and recording the track for which, outside France, she is still most famous.

The duet "Je t'aime (moi non plus)", featuring Birkin faking an orgasm in what Gainsbourg called "her choirgirl voice", was banned by the BBC, denounced by the Vatican, and scandalised the world, guaranteeing that it sold by the million. She considered, she says, translating it into English to perform on this tour, until she realised it came out as "I come and go in between your kidneys". Perhaps there's another reason it didn't make the cut: which part would she play?

The long ironed hair of 1969 is now a bouncy shoulder-length, but she's otherwise instantly recognisable: that iconic dentition, those cheekbones which, were they any higher, would be her eyebrows, and not a gram of fat on her bones. You can see why Hermès named a handbag after her. And if anyone has a right to sing Gainsbourg, she does. "L'Amour des feintes" was written for her, "Jane B" – based on Chopin's Prelude No 4 –was about her, and as for "Ah Melody", from his revered, Lolita-inspired concept album Histoire de Melody Nelson? Jane Birkin was Melody Nelson.

Her all-Japanese band are superb, in particular violinist Hoshiko Yamane, who gleefully squeals Brigitte Bardot's bits on "Comic Strip", her "shebam, pow, blop, whizz!" threatening to shatter the skylights. And Serge's versatility – from hard bebop to sentimental chanson to light reggae – is a challenge from which they do not shrink.

Rita Ora describes "Hot Right Now", the chipmunk-cheeked, Kosovo-born singer's chart-topping collaboration with DJ Fresh, as "the song that changed my life". To illustrate how much her life has changed, she shows a video montage of weeping fans having their T-shirts signed. And there's the rub. They've changed her life. She'll never change theirs.

Rita Ora, you see, could be anyone. Sure, she has a big, ball-busting Taylor Dayne voice when she wants to. And she's got the big, thumping, dancefloor-ready pop anthems to match (not that she wrote any of them). But the Sylvia Young-schooled former Eurovision entrant has no special charisma. If it wasn't her on stage at the Manchester Academy, it'd be someone else.

There's something a bit Poundland about the presentation. She enters in a plywood radiation-hazard "quarantine" crate, surrounded by silver barrels (of uranium ora?), that looks like it was knocked up by an am-dram group. The impression that she's Gaga on a budget isn't helped by the Bacofoil space suit, or indeed the full-face T-shirt on the merch stall.

Every box is dutifully ticked. There's rose-petal confetti. There's some stand-up drumming. There's the most hateful moment of every pop concert – the acoustic interlude – featuring a cover of "Hey Ya" which seems to miss the entire point of the song, and the obligatory fan-plucked-from-the-crowd. And, bafflingly, there's a tribute to Biggie Smalls, who died when Ora was six.

It has to be said that the kids are going crazy. But the kids' hysteria is all their own work, their own admirable determination to have fun. Rita Ora just happens to be the excuse for it. She'll do for now, till the next one comes along.

Critic's choice

Elegantly besuited synth duo Hurts begin their comeback at Heaven, London (Thu). Meanwhile, this year's NME Awards tour, featuring Django Django, Miles Kane, Palma Violets and Peace, starts rolling at the Academy, Newcastle (Thu); Academy, Manchester (Fri) and Academy, Leeds (Sat).