It is the question dividing viewers of The Crown: is Gillian Anderson’s portrayal of Margaret Thatcher sympathetic or sneering?

Now Anderson has disclosed her own feelings about Britain’s former leader, admitting that she was no great fan of Baroness Thatcher’s “dictatorial” style and suggesting that she had turned “mad” by the end of her premiership.

“I wouldn’t necessarily agree with her leadership style,” Anderson told Harper’s Bazaar.

“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.”

Anderson conceded, however, that Baroness 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 are a supporter of hers or not, or like her or don’t like her, you can’t let go of the fact that she really made herself,” she said.

To begin her preparation for the role, Anderson delved into Baroness Thatcher’s childhood.

Gillian Anderson on the cover of December's Harper’s Bazaar

Credit: Harper’s Bazaar/Oliver Holms

“Childhood is always a very helpful and informative place to start. Margaret Thatcher grew up as a grocer’s daughter and as an alderman’s daughter – a Methodist – so all of those aspects defined who she was as Prime Minister, her policies and how she budgeted for the country. She built her world; she really worked hard to get where she was,” Anderson said.

She added that she had taken on the role because “I think I’m more attracted to women who have something to say or are quite determined, because I tend to be quite determined myself.”

The Crown’s writer, Peter Morgan, had to rely on his imagination to script scenes between Baroness Thatcher and the Queen during their weekly audiences.

He has faced criticism from royal commentators for making up dialogue in the first episode, showing Lord Mountbatten scolding the Prince of Wales for his affair with Camilla Parker Bowles and writing a letter to the Prince instructing him that he must marry “some sweet and innocent, well-tempered girl with no past”.

Morgan said he had made up the letter but “everything that’s in that letter is what I really believe, based on everything I’ve read and people I’ve spoken to, represents his view.”

The December issue of Harper’s Bazaar is on sale now.