As the dimming lights silhouetted a black-garbed horn section filing quietly onstage, and a deep blues hook and chomping backbeat powered up for the guitar-toting woman in shades at the microphone, it was plain that Melody Gardot, the smooth chanteuse, was long gone.

Five years ago, she would sit demurely on stage to deliver her imaginative lyrics in a luminous whisper, Lauren Bacall-style blond mane over one eye – which made her a star, but was also a legacy of the teenage bike crash that had made loud noises and easy movement intolerable. But with this year’s Currency of Man album, Gardot has shaken loose a soulful, hard-rocking, ruggedly upbeat sound with trenchant new lyrics.

She was blithely dancing to James Brown-like sax riffs by the finale, and the crowd (Gardot was playing a rare club gig for the Pizza Express jazz club’s 50th anniversary) was looking for any patch of floor it could find to do the same.

Gardot sang just one fragile ballad in her earlier meticulously nuanced manner - Baby I’m a Fool, from My One and Only Thrill. Otherwise, her long, single set boiled with infectious grooves, and vocals that veered from drifting ambient tones to scalding Nina Simone-tinged declamations. She swept through wordless improv swerves from the betrayal lyrics of the opening Same to You, suggested Peggy Lee’s Fever sung by Tom Waits (shadowed by the excellent Irwin Hall’s free-jazz sax lines) on Bad News, and played piano on a mostly instrumental tribute to Charles Mingus.

Gardot’s remarkable voice took on the slide of a sitar on Morning Sun; she swapped lines with the audience on a New Orleans blues shuffle, threaded soft, yodelly phrases through the band’s choral vocals on Preacherman, and had the horn section stripping off their jackets for the funk gyrations of the finale. If the posters outside hadn’t had “Melody Gardot” written on them, I would barely have believed it.

• At the South Bank, London, on 17 November in the London jazz festival.