Natalie Portman and Scarlett Johansson struggled to learn the Queen's English

American actresses Natalie Portman and Scarlett Johansson claim mastering the Queen's English was the toughest challenge while filming their latest movie.

Portman, 26, plays Henry VIII's second wife, Anne Boleyn, and Johansson, 23, her sister, Mary, in The Other Boleyn Girl.

The pair admitted it was tough perfecting their accents, particularly while wearing corsets.

The movie is heavy on dialog, so Portman worked with a dialect coach for a month before shooting.  "That was a big challenge. One of the biggest challenges, personally," Portman said.

"It totally takes me out of a movie when I hear British actors doing a bad American accent. It's a scary thing. I can't improvise with an accent at all."

For Lost In Translation star Johansson, speaking the Queen's English was "something you want to nail down early so it's not something you think about when you're working. I've spent a lot of time in London and having family there, that was helpful for me. It's definitely a hurdle."

She said the language barrier was one reason the pair, working together for the first time,  "clung to one another" during filming.

"I feel like I got so much of my energy from Scarlett," Portman said.

"When I was like, 'What am I doing? Where am I?' I'd look at her and be like, 'OK. She's my sister.'"