Kate Beckinsale is said to have demanded a butt double for her latest move – because she thinks she's fat.

Producers on Whiteout have had to hired a $2000-a-day model to stand in for the star after she refused to bare her rear in shower scene.

A source tells Britain's The Mail On Sunday, "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.

Does my butt look big in this? Kate's tiny rear

"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."