The Crown actress Gillian Anderson has said she is no great fan of Margaret Thatcher's "dictatorial" style and suggested she had turned "mad" by the end of her time in power.
"I wouldn't necessarily agree with her leadership style," Anderson told Harper's Bazaar magazine.
"By the end I think she became quite dictatorial. She was in power for 11 years, and they say that leaders should never go beyond seven years or they start to go mad."
The X-Files star portrays the late British prime minister alongside Olivia Colman, Emma Corrin, Helena Bonham Carter and Tobias Menzies in the fourth series of the hit show.
Anderson conceded that Thatcher had "the most extraordinary mind".
The actress also said she admired the fact that a grocer's daughter had risen so far.
"Whether you're a supporter of hers or not, or like her or don't, you can't let go of the fact she made herself," she said.
To begin her preparation for the role, Anderson delved into the controversial politician's childhood.
"Childhood is always a very helpful and informative place to start," she said.
"Thatcher grew up as a grocer's daughter and a Methodist, so those aspects defined who she was as prime minister, her policies and how she budgeted for the country.
"She really worked hard to get where she was."
Anderson said she took on the role because "I think I'm more attracted to women who are quite determined".