She was introduced on stage by Sporty Spice Mel C – one of her music heroes.
The Voice mentor admitted she was a huge fan of the Spice Girls growing up, especially Mel.
She said: “I was always Sporty Spice – I’ve been backstage singing Zig-a-zig-ah and Two Become One.
“If only I had known what that was really about at that stage.”
Jessie performed three acoustic songs to kick off Music Is GREAT week at HMV in Oxford Circus, London