Stewart-Jarrett - best known for playing Curtis on E4's Misfits - joins conspiracy thriller Utopia, which also stars Alexandra Roach (The Iron Lady), Geraldine James (The Girl with the Dragon Tattoo) and Michael Smiley (Luther) and will air in 2013.
Lloyd, whose past credits include Game of Thrones, Doctor Who and Robin Hood, will appear in four-part drama The Fear.
The Brighton-set drama is led by Tyrannosaur actor Peter Mullan and follows crime boss Richie Beckett as he struggles with a mafia feud, early onset dementia and issues within his own family.
Forthcoming Channel 4 drama The Coup has been renamed Secret State - Gabriel Byrne (The Usual Suspects, In Treatment) will be joined by Douglas Hodge (Robin Hood), Gina McKee (Line of Duty), Rupert Graves (Sherlock) and Charles Dance (Game of Thrones).
Beaver Falls actor Arsher Ali meanwhile joins Spooks star David Oyelowo in terrorism drama one-off Complicit from writer Guy Hibbert, which also stars Appropriate Adult BAFTA winner Monica Dolan.
Further castings include John Simm (Mad Dogs) and Shirley Henderson (The Crimson Petal and The White) in Michael Winterbottom's one-off drama Everyday and Harry Potter's Katie Leung in four-art drama Run alongside Twenty Twelve's Olivia Colman and The Walking Dead's Lennie James.
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