Dame Helen Mirren wept when she saw the costumes for her Oscar-winning role in The Queen, fearing that she would never be able to understand a woman who wore tweed skirts and sensible shoes.

Speaking at The Times Cheltenham Literature Festival yesterday, Dame Helen confessed that, as a “girlie woman who loves dressing up”, she did not relish the thought of wearing Barbour jackets and Hermes scarves.

In front of a 1,300-strong audience, she said: “The Queen is so much a part of my parents’ generation and so much a part of the history and culture of Britain that although they were fervent antimonarchists it was very hard not to like her. But when I came to the costume fittings I literally cried.

“I’d just done Elizabeth I - that had been a trip into fantasyland. We shot it in Lithuania and they had made all this jewellery, pearls and diamonds and sapphires and they laid it out on a table in my dressing room. I dressed myself up like a Christmas tree.

“To go from that to the brown shoes and tweed skirts, Barbour jackets and Hermes scarves, I found it very hard to be someone who chose to wear these clothes. I thought I would never be able to understand this woman.”

Dame Helen went on to win an Oscar for her performance in the film, which was directed by Stephen Frears and written by Peter Morgan. In total, the film won 55 awards across the globe, including four Baftas.

Although Dame Helen initially had her doubts about the role of Elizabeth II, her worries were assuaged once she had completed the costume fittings.

She told the Cheltenham audience: “We had a very good costume designer and if it was a tweed skirt it was the best you could get, had a lining inside of beautiful silk and fitted me to the millimetre with a bit of padding that I was wearing. The fit of everything was perfect and then I understood what it felt like to be the Queen.

“I absolutely grew to love portraying someone unlike me who is not vain on that level in the slightest. She has all the diamonds in the world but she is at her happiest in old wellingtons and an old Barbour.”

In order to prepare, Dame Helen had to cram her research into a fortnight’s break between finishing shooting on Elizabeth Iand the start of filming on The Queen.

She said: “I went to France for a week with all these tapes of documentaries about the Queen and I read lots of books and then I was utterly intimidated at the thought of it. I’m not a very good mimic at all.” She added: “I was more than liking the Queen by the end. I grew in the end to love her.”

Despite portraying the Queen, Dame Helen has met her only once, “a long time ago”. “I was invited to dinner at the palace [after the film came out] which was a big thing for me . . . but I couldn’t go. I was working in South Dakota, I had to call up and say I couldn’t come, which was mortifying and upsetting but I hoped she would understand what it is to be a hard working woman.”

Dame Helen’s busy schedule meant that she was not able to confirm her appearance at the The Times Cheltenham Literature Festival until a month ago. She is promoting her new book, In the Frame: My Life in Words and Pictures, a memoir which includes accounts of her Russian ancestry and early career in experimental theatre.

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