Nicole Kidman - who stars in the BBC's forthcoming second series of Jane Campion's Top of the Lake  - declares that " motherhood brings you to your knees."

"It’s surfacing in pretty much everything I do," the 50-year old actress tells The Sunday Times today. In Top of the Lake: China Girl she plays a mother who has a conflicted relationship with her adopted daughter, played by director and writer Jane Campion’s daughter, Alice Englert, 

Kidman spoke about being a mother and indeed about playing mothers. There have been quite a few maternal roles since her outstanding role in  Alejandro Amenabar’s film The Others. 

"The strongest force I can find within me, right now, is the maternal force," she says. "Romantically, I’m obviously incredibly awake and alive. I have a really, really strong, good marriage. " She is married to country singer Keith Urban.

Kidman suffered two miscarriages, had two adopted children with Tom Cruise, an `unexpected late pregnancy' with Urban, and a fourth daughter, born through a surrogate arrangement some years back. Top of the Lake: China Gorl deals with surrogacy, which in the actress's native Australia is still illegal - there is a black market.

"Jane said to me, ‘Would this be a difficult place for you to go in terms of what the theme of this is?’ And I said, ‘No, because my story seemed very different.’ Mine was agreed upon, and it was a beautiful thing that a woman chose to give us. It was an incredible gift she made."

Nicole Kidman with husband Keith Urban