The actor, 37, will portray a younger version of the Albert Square matriarch in a special instalment of the BBC soap set in the winter of 1979.
"I did sort of speak to her and say you know, 'Is this the right thing for me? Am I allowed to do it?'" said Winstone.
"And I had a few signs."
Winstone – who previously played Dame Barbara in the 2017 biopic Babs – went on: "I felt like, she'd always say to me on set when we did Babs is, you know, 'You are more me than me'."
The actor said she also had a "deep chat" with her agents about the part.
"But when it’s an opportunity like this – Peggy Mitchell, the landlady of our nation – it’s an honour for me," she added.
📣 BREAKING NEWS! 📣 Jaime Winstone is set to play a young Peggy Mitchell in a special flashback episode of #EastEnders that centres around the Mitchell family. To find out more, please visit @bbceastenders on Instagram and Facebook. pic.twitter.com/X4x2iTkiLT
— BBC EastEnders (@bbceastenders) July 26, 2022
She went on: "It took a long time to shake that wiggle and that giggle, but I got to implement all the stuff personally with Barbara… I got to see her at home and I got to sit around the piano and sing with her.”
“She was so gorgeous and so generous with her time and had so much love and energy," she went on.
The star said the episode is "about the family before the Mitchells became the Mitchells".
"It’s set in 1979, the backdrop is London, grim, they are quite skint, there’s rubbish on the streets… and different for women then, women knew their place and did the cooking, the cleaning and were very proud home keepers," she said.
Winstone also said it was a "turbulent" instalment and would show a more vulnerable side to the Queen Vic landlady.
"It’s the making of how Peggy Mitchell became Peggy Mitchell," she explained.
The EastEnders special will air on BBC One on 5 September at 7.30pm.
This Morning airs weekdays from 10am on ITV and ITV Hub.
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