As announced last month, the former Bad Girls actress has taken over the role of Lorraine, who is the mother of Walford minx Mandy (Nicola Stapleton).
Lorraine returns to Albert Square after exchanging a series of text messages with scheming Lucy Beale (Hetti Bywater), who wrongly suspects that Mandy's mystery contact 'L' must be a secret boyfriend.
Teasing Lorraine's arrival, Alcock told TV Choice: "There will be a collective intake of breath from viewers because just when you think she couldn't stoop any lower, she goes full-steam ahead.
"Many Albert Square residents didn't think there was a bigger leech than Mandy, but we see where she gets it from now. She has no qualms and she's proud of it."
She continued: "Allegedly she let some awful things happen to Mandy, which may come out in time. I think viewers are interested in the broken shells of a character and she's definitely a broken shell."
However, Alcock added that she wants Lorraine to be seen as more than just a villain.
"You're not just made that way, something happens to make you like that," she commented. "I reckon she was abused, and the abused often then become the abuser, and unfortunately that vicious circle has not been broken. I've tried to play her with a few levels."
EastEnders airs Lorraine's return scenes on Thursday, March 1 at 7.30pm on BBC One.
> EastEnders return for Mandy Salter's mother
> EastEnders: Pictures of Lorraine's return
> EastEnders' Mandy in turmoil over mum Lorraine - Spoiler Pictures
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