Truth is the story of American TV news producer Mary Mapes, who won a Peabody Award for breaking the Abu Ghraib story and went on to investigate President George W Bush's inconsistent service record in the National Guard. "Truth happened like a bolt from the blue," she says. "I read it, I ate it alive, and it got up incredibly quickly."

Cate Blanchett stars as the award-winning journalist Mary MapesCate Blanchett stars as the award-winning journalist Mary Mapes

The film traces how the Bush story was torn apart by the media, discrediting Mapes and ending the career of veteran TV newscaster Dan Rather, played by Robert Redford. Blanchett looked up Mapes' interviews after the scandal. "She was clearly in lockdown at the time," Blanchett says, "and when I met her I found it very difficult to reconcile that Mary to this incredibly vivacious, vital, vibrant, hilarious, front-footed go-getter. I thought somewhere between the two lies Mary. But she was very generous, very self-deprecating, very wry and very, very passionate and full of heart."

Truth opens this month in America, with Carol released next month. Both are Oscar-calibre performances, but Blanchett can only be nominated for one of them and refuses to pick a favourite. "I hope people go and see Carol," she says. "I think the power of that film was that, yes, there's two women falling in love in the '50s, but it really is a film about falling in love. Gender, in a way, becomes an obstacle, but it's not the only obstacle. Their age gap is another one."

Watch the trailer for Truth:

She loved working with director Todd Haynes again, after starring in his inventive 2007 Bob Dylan biopic I'm Not There. "He's made such a subtle, beautiful, textured, layered beast of a film," she says of Carol. "And then in the same year to be offered a role like Mary, with subject matter that's very relevant and still dangerous, and to be working opposite Redford. I'm sad in a way that they're coming out on top of one another, but I just hope they can both find their audience."