This full-on celebration of soulful revolution is conclusive proof that it ain't over till the fat lady sings.

The fat lady in question is Jennifer Hudson, onetime runner-up in American Idol and the main draw in this overlong tribute to the groundbreaking days of Motown.

Her heavyweight role of wannabe soulstress Effie steamrollers poor old Beyonce, who stays timidly polite throughout the machinations of a plot that closely resembles that of Diana Ross and the Supremes.

They're both belters in The Dreamgirls, a trio of sirens (the third is Anika Noni Rose) who get their break on the Detroit "chitlin circuit" as backing singers for lothario James "Thunder" Early (Murphy).

Pushed by used car salesman-turned-manager Curtis Taylor (Foxx), they're relaunched as a solo act...but the easy-on-the-eye Deena (Beyonce) has replaced the chunky chanteuse on lead vocals.

Understandably hurt, the discarded diva quits the group...but not before she's belted out a ground-trembling version of And I'm Telling You.

Based on the award-winning Broadway phenomenon, this cannot shake off its theatrical roots and remains resolutely welded to the original stage musical.

With Chicago, director Bill Condon cleverly worked the big performance numbers alongside the narrative sequences but here it's as if the whole show takes place in front of the stalls.

If we're being honest Beyonce is supposed to be Diana Ross while Foxx is the Berry Gordy-style svengali who engineered her pre-eminence in the group.

However, while you can buy Hudson as the discarded star Beyonce is less convincing, delivering a blank performance where there should be fight and fire.

Condon's sparkly, over-the-top production does not so much convey the creative powerhouse that was Motown in its heyday but a sequinned Las Vegas revue that's overdosed on steroids.

On the plus side, Murphy is never less than engaging as a Little Richard/James Brown amalgam of stagecraft and passion while there's some subtle (not a word you'd expect to see in this film) nods to the innocence of the fledgling Jackson Five.

Don't go expecting an insight into the celebrity condition: it's an unashamed crowd-pleaser - a sort of Sunday Night at the Detroit Palladium.

Tim Evans