The star of dark and racy period drama "Lady Macbeth", Florence Pugh, says playing the new British film's protagonist was terrifying, not just because her character was so complex but because she herself was scared of her.

Pugh, listed among Breakthrough Brits by the British Academy of Television Arts (BAFTA) in 2016, plays Katherine, a young woman, stifled by her loveless marriage to a much older man and abused by her grim new family.

"I knew Katherine was an incredible character but I also knew that the job behind her was huge and it did terrify me because there was a lot of her to tackle in just one film," Pugh told Reuters.

"But for me that really excites me, when a character kind of scares me," she said.

The film charts the violent lengths to which Katherine is willing to go to protect her newfound freedom after she starts an affair with a groomsman (Cosmo Jarvis), a relationship that starts when her husband Alexander (Paul Hilton) and controlling father-in-law Boris (Christopher Fairbank) are away on business.

For Pugh, however, some of the film's most interesting aspects were other people's reactions to Katherine's dark side.

"Some of the features about Katherine that really excited me was that throughout the entire film she goes beyond herself and hurts a lot of people and we still love her, we still root for her, we still want her to succeed," she said.

"Lady Macbeth" opens in the UK on Friday and in U.S. cinemas in July.