Cate Blanchett will go to great lengths for her film roles - but she refuses to expose her naked behind.

While she's happy to do almost anything for her craft, including dressing up as a man for her portrayal of Bob Dylan in I'm Not There, this mum of two draws the line at baring her naked behind on the big screen.

When Cate was asked to return to her Oscar-nominated role of Queen Elizabeth for the new movie Elizabeth: The Golden Age, she was happy to rise to the challenge. But when the actress realised the queen would have to bare her bottom on screen, she decided it was time for a double.

Director Shekhar Kapur tried to convince Cate to expose her backside but the strong-minded antipodean refused.

'It's not me up there. It's not my bottom - it's someone else's,' Cate reveals. 'Shekhar had his reasons, but I wasn't convinced. Only my husband sees my bum.

A source on set says: 'A butt double was called - it was the only way she'd agree to do it.' And while baring all on the big screen isn't on the cards any time soon for the beauty, Cate's hubby Andrew Upton will be seeing a bit more of his wife's derriere now that the family has set up base in Australia.

According to sources close to the talented actress, Cate's got plans to expand her family now that life is a little more settled. And with her elder son Dashiell settling into school in Sydney and her younger son Roman reaching the age of three, she's got it in mind to try for a girl.

'The timing's perfect for Cate and she's never made any secret of the fact that she'd love more kids,' a close friend says. 'Cate's determined to have four and has spent the past year talking it over with Andrew and he's up for it.

'Cate's going to be spending a lot of time in Sydney, only going abroad for a couple of trips a year. Now that they've made this big commitment to the boys' future and stability, Cate thinks they may as well make the most of it.'

And her desire to add to her family is so overwhelming that the actress, who usually plays her personal cards very close
to her chest, even let slip in a recent interview that falling pregnant is something she is actively hoping for every month.
'Andrew and I are not going to wait forever,' Cate laughs. 'God, I'd love it to be now. I'd love it to be next week.'