Actress Sienna Miller was forced to wear fake breasts for her role in forthcoming action movie G.I. Joe - because her own cleavage was not big enough for director Stephen Sommers.

The Alfie star joins Dennis Quaid and Brendan Fraser to play femme fatale The Baroness in the upcoming movie, which is based on the popular U.S. play figure and TV series.

But Miller admits she was left slightly stunned when Sommers told her her small chest had to be given an extra boost so she would look more curvaceous on screen.

She says, "(I wear a) tight black leather outfit. And much bigger boobs.

"They gave me these things that looked like chicken fillets. The director said, 'I'm gonna be honest, I like girls with big boobs', and I don't have them so we made them bigger.

"At least he's honest. But I was mildly offended."