Starring Matt Berry and written by Andy Riley and Kevin Cecil with additional material by Berry, the IT Crowd actor stars as Detective Inspector Rabbit, a "hardened booze-hound cop" in Victorian Whitechapel.
Channel 4 adds: "He's aided and abetted by his new partner Wilbur Strauss (Freddie Fox) and the country's first female police officer, Mabel Wisbech (Susan Wokoma), as they bring justice to the streets of the East End."
Production is currently under way on the six-part sitcom, which is expected to broadcast later this year.
Keeley Hawes said: "It's great to be working with Matt, Susan and Freddie on such a brilliantly original show. Lydia is such an enigmatic character. It's been a thoroughly enjoyable, bonkers experience."
Sally Phillips commented: "I can report that there is literally nothing more pleasurable than playing a haughty, 19th Century, pansexual, Bulgarian autocrat with access to guns. I may have peaked."
Initial images of key supporting cast members Armstrong, Halfpenny, Phillips and Hawes have also been released:
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