The mystery drama - which stars Anna Maxwell Martin, Rachael Stirling, Sophie Rundle and Julie Graham - returns for a new series on Monday (January 6).
Outnumbered's Hattie Morahan joins the cast for the new series, which will be comprised of a pair of two-part stories written by series creator Guy Burt.
Set a year on from the first series in 1953, Jean (Graham), Susan (Martin), Millie (Stirling) and Lucy (Rundle) reunite when former Bletchley Park colleague Alice Merren (Morahan) is accused of murder.
ITV described The Bletchley Circle as a "wonderful addition to our drama slate" when announcing the second series last May.
ITV's Director of Drama Commissioning Steve November said: "The Bletchley Circle is a wonderful addition to our drama slate last year and we're delighted that it's returning to ITV with two new and exciting stories."
Jamie Payne (Doctor Who) will direct the opening two-part story, with Sarah Harding (Queer as Folk) helming the second.
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