In the pantheon of soul divas, Chaka Khan is surely one of the fiercest. With a soaring, multioctave vocal range that earned accolades from Aretha Franklin and Miles Davis, as well as a chequered personal life and a stint in the Black Panthers alongside Fred Hampton, Khan’s story has long felt ripe for immortalisation in a jukebox musical.

I’m Every Woman features X Factor winner Alexandra Burke in the lead role, with a book by Khan’s own creative director, Nia T Hill. Running just shy of three hours, it is a gargantuan undertaking of two uneven parts.

The opening half sprints through a remarkable girlhood and young adulthood. Khan’s father leaves the family owing to a drug problem, she joins the local Black Panther party chapter in Chicago, falls in love, decides to become a singer and witnesses Hampton’s murder – all in a matter of minutes. Celebrity impersonations pop up in case the frenetic pace isn’t enough to hold the audience’s attention – from a spirited Joni Mitchell to vapid parodies of Prince, Stevie Wonder and Miles Davis.

Burke plays Khan with an energetic youthfulness – but when it comes to vocals faces a sisyphean task. She makes a valiant effort of singalong hits like Ain’t Nobody and Tell Me Something Good, but lacks the resonance to replicate Khan’s power. Nowhere is this clearer than during the ballad Through the Fire, which employs three singers to replicate Khan’s performance and still falls short of her key-jumping agility.

Director Racky Plews’ staging is nimble, making use of immersive projections, while the ensemble boasts a comic star in Ashley Stroud, as Khan’s bolshie younger sister, Taka Boom. Yet when the second half arrives and Khan finds herself the “Queen of Funk” in the 1980s, the show runs entirely out of pace and music.

The Prince-penned I Feel for You is a raucous post-interval opener, but the remaining hour meanders through Khan’s 90s and 00s years, choosing to focus on her charitable foundation work and efforts to go independent, rather than her artistry. When it comes time for a harried emotional reunion with her estranged daughter in rehab, the pathos refuses to land. Instead, I’m Every Woman becomes a musical in service to somewhat sparse music, rather than a clearly astounding story.