ONE of the most shocking episodes in Swindon’s recent history is to be played out on TV screens in a new drama series.

Martin Freeman and Imelda Staunton are to star in the six-part drama that tells the story of how Det Supt Steve Fulcher deliberately broke the rules and caught the killer of Sian O’Callaghan and Becky Godden, costing him his career and reputation.

Due to be shot partly in Wiltshire, the cast of A Confession also includes This Country’s Charlie Cooper.

Screenwriter Jeff 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 roughshod over the law?”

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Sian’s mum Elaine Pickford said she was not able to talk to the Adver at the moment. “It is obviously something that I’m aware is happening, but I’m not able to comment,” she said.

The series will follow events after 22-year-old Sian’s disappearance in March 2011, when she set out on the short walk home to her boyfriend Kevin (Cooper) after at night out. When she fails to arrive and does not answer his increasingly frantic texts, he alerts the police who turn up at the home of her mum, played by Cold Feet actor Siobhan Finneran.

It traces the investigation, which senior investigating officer Det Supt Fulcher (Freeman) believes is a race against time to find Sian alive.

While his team closes in on the main suspect, taxi driver Christopher Halliwell, Karen Edwards (Staunton), the mother of Becky Godden, who went missing in 2003, sees the local news and begins to believe her daughter is involved in some way. And although they don’t realise it, the two mums live back to back.

The series reaches a dramatic high point when the policeman has Halliwell, played by Joe Absolom, driven to Barbury Castle near to where he believes Sian is being kept, instead of taking him into custody and given access to a solicitor.

In the real life investigation Halliwell and Fulcher talked for four hours before the killer confessed and offered to show the detective where Sian’s body was. They drove to the White Horse at Uffington where Halliwell decided to admit killing Becky. Her remains were found in a field at Eastleach.

By not taking the suspect to custody and offering him access to a solicitor, Fulcher had broken the rules of the Police and Criminal Evidence Act.

The taxi driver was convicted in 2012 of Sian’s murder and sentenced to life with a minimum of 25 years. But because of the rule breach, the charge of murdering Becky was dropped.

It was four years before he was tried and eventually found guilty of the 2003 killing.

During the trial he admitted he made the confession because he knew the rules had been broken and he wanted to destroy the detective’s career.

In the meantime Det Supt Fulcher’s actions were examined by the Independent Police Complaints Commission and he was found guilty of gross misconduct.

He kept his job but resigned in 2014, later saying he suffered stress and had to take anti-depressants.

Becky’s mother was one of those who supported him, saying at the time: “He is and will always be my hero and I will always be eternally grateful.

“I have such admiration for him, I have said it many times before if he had stuck to Police and Criminal Evidence (PACE) rules then neither my daughter Becky nor Sian would have been found. Steve Fulcher gave two families back their two daughters and we were able to put them to rest.”

The series, co-produced by ITV and Urban Myth Films, will be

directed by Paul Andrew Williams, whose previous work includes Broadchurch.