The Pitch Perfect star reveals she has agreed to take on a small part in the film, based on the hit U.K. TV show of the same name and starring Jennifer Saunders and Joanna Lumley.

Rebel admits she offered to work without payment and was surprised when the favour was called in.

"I'm actually doing a movie for a favour in a couple of weeks. I'm gonna film the Absolutely Fabulous movie in London," she tells Australian radio's Kyle and Jackie O Show. "It's just a little cameo as a favour...

"It's huge in the U.K. and I did that thing where you go up to someone who you really admire and say, 'If you ever ever need me for a movie or anything I'll do it for free' so now I have to go all the way to London... for no money."

The long-awaited film is set to be a star-studded affair as it already boasts appearances from supermodel Kate Moss, Spice Girls singer Emma Bunton, model David Gandy, and Lulu, while other stars rumoured to be appearing include Kim Kardashian and Glee's Chris Colfer.