Martin Freeman is a busy man; a day after revealing he is making a parenting comedy for FX and Sky, the Sherlock star is making a six-part drama for UK’s ITV.

Studiocanal’s Urban Myth Films will produce A Confession, along with ITV Studios, with Imelda Staunton also starring.

Written by Jeff Pope, the series tells the story of how Detective Superintendent Steve Fulcher, played by Freeman, deliberately breached police procedure and protocol to catch a killer, a decision that ultimately cost him his career and reputation.

Set in Swindon, Wiltshire, A Confession, details the disappearance of 22-year-old Sian O’Callaghan in March 2011. On a night out with girlfriends, Sian left a nightclub in Swindon Old Town to walk the 15 minutes home to boyfriend Kevin Reape, played by Charlie Cooper (This Country). Worried for her safety, Kevin reports Sian missing when she fails to come home in the early hours or respond to his increasingly frantic texts.

With the police investigation underway, officers arrive on the doorstep of Sian’s mother, Elaine O’Callaghan, played by Siobhan Finneran (Happy Valley), who at first thinks her daughter must have stayed overnight with a girlfriend. Described as a family girl, it was uncharacteristic of Sian to be out of touch with her loved ones.

Senior Investigating Officer Steve Fulcher leads a team which begins to piece together Sian’s last movements, scouring CCTV footage from the club and re-tracing her steps home. Cell-site analysis reveals her mobile phone signal bouncing off a mast 14 miles away in Savernake Forest. With the missing person’s enquiry in full swing Fulcher, orders a full-scale search operation.

Meanwhile, Karen Edwards, played by Staunton, the mother of Becky Godden, a 20-year-old who disappeared a decade previously in 2003, is watching the investigation unfold on the local news and in the town centre. Reminded of Becky’s disappearance, she becomes gripped by fear that her daughter will somehow be involved in what is unfolding before her eyes as the search for Sian goes on.

Paul Andrew Williams (Broadchurch) directs all six episodes with Pope exec producing alongside Johnny Capps and Julian Murphy and Tom Dunbar as Producer.

Pope said, “I found this is a fascinating story to tell on a number of levels. On one hand it is a brilliant piece of detective work, but in order to find both girls Fulcher felt he had to deny Halliwell his rights as a suspect. It brings into question how we want our police to behave when someone goes missing. Should Fulcher have been praised as a courageous officer fighting for the life of a girl, or lose his career for riding rough shod over the law?”

ITV Head of Drama Polly Hill added, “It is wonderful to be working with Jeff Pope again on this compelling and important true story. I’m delighted that the brilliant Martin Freeman and Imelda Staunton are leading the cast, making this an unmissable drama for next year.”

ITV Studios Global Entertainment will distribute the drama internationally.