The former Hollyoaks actress was cast in the long-running medical drama earlier this year in the role of Tamzin Bayle, a new paramedic who joins the team in tomorrow night's episode.
Atkinson told TV Times of how she landed the part: "I did a workshop with the BBC, where I sat down with producers and directors and they asked me what sort of character would I like to play if I were to join Casualty.
"I thought the obvious choice would be a nurse so I said a paramedic, as I thought that would be something a bit different. They went away and then they called me back a few weeks later and said that they'd like to write me into the series."
Atkinson said that there are clear differences between Tamzin and Lisa Hunter, the character she played on Hollyoaks for five years.
"I think Tamzin's a lot more clued up in life than Lisa," the 26-year-old commented. "She's a lot older and wiser, but she's still got the girl-next-door charm that Lisa had, which is great."
Casualty continues tomorrow night at 8.35pm on BBC One.
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