Producers have had to hire a £1,000-a-day nude stand-in after Kate, 34, refused to bare her derriere in a shower scene.
In the past the actress, who earns £3.2million for a film, has not been shy of squeezing into sexy clothing and almost showed her bottom in Uncovered in 1994.
Does her bum look big in this? A slimline Kate at a premiere
But a source on her new film Whiteout said: "Kate has a terrible self-image. She thinks she is fat and she is always complaining how certain outfits make her bottom look big. Of course, the reality is that she has the most amazing body.
"The script called for her character to be filmed nude in a shower, focusing in on her bottom and thighs. Kate insisted on a double being hired. She was quite open on the set about not liking her body and said she particularly loathed her bottom and was not comfortable baring it."
A last-minute call for a double went out on a Hollywood casting website last week for scenes that begin shooting tomorrow.
Silver Pictures advertised for a 5ft 8in brunette, weighing just under 9st. It added: "It’s a shower scene so there is no intimacy."
Barely There: Kate allowed just a hint of her bottom in Uncovered in 1994
Kate plays a US marshal tracking a killer in Antarctica in the £25million drama.
The source explained: "Kate just didn’t want to show her bottom, even though everyone on the set was saying how good it looks in jeans. She said she couldn’t face the thought of seeing her butt up on a big screen. She will have the final veto over who stands in for her."
Oxford-educated Kate, whose father, Porridge star Richard Beckinsale, died aged 32 in 1979, suffered anorexia as a teenager and at 15 weighed just 6st.
She has openly discussed her body image issues and recently complained of the unrealistic pressure on women in Hollywood.
She told US Glamour magazine: "I don’t think you can aspire to the Hollywood 'look' and nor can I.
"Everybody is retouched, stretched, lengthened, slimmed and trimmed. I could look at a picture of myself from the past and think, 'Why don’t I look like that now?' It’s because I never have. If I could swap places for a day it would be with someone with gigantic, real breasts. I am fascinated by breasts because my mother didn’t have them either."
She is not the first star to have a bottom double. Keira Knightley had one in Atonement and Sarah Michelle Gellar demanded one for Scooby-Doo.
