A DRAMA about Britain's first female serial killer will be filmed in the region from August, with Downton Abbey actress Joanne Froggatt taking the lead role.

Dark Angel tells the story of poisoner Mary Ann Cotton, who was hanged in Durham Jail in 1873 for the murder of her stepson - although her victims were thought to number as many as 21, including her own mother and children.

Miss Froggatt, who was brought up near Whitby and is best known for her role as kind-hearted lady's maid Anna Bates in Downton Abbey, will play Cotton in the two-part drama, to be filmed in North Yorkshire and County Durham.

It is based on a book on Cotton's life written by criminologist David Wilson.

Miss Froggatt posted a picture of the book on her Twitter page over the weekend, saying: "Doing some research for my next role."

Cotton was born in Houghton-le-Spring, Sunderland, in 1832. She married four times, although her fourth marriage was bigamous, and three of her husbands died of mysterious stomach complaints - thought to have been caused by arsenic poisoning.

Up to 14 of her own children and stepchildren are also thought to have been poisoned, as well as her mother, lover, and sister-in-law. Cotton's method of administering the drug was said to be via tea poured from a pot during her 20-year murdering spree.

She also collected insurance payments from two of her husbands' deaths, and benefited from her lover's will.

The "functioning psychopath" was finally caught when a post mortem was carried out on her stepson by a suspicious doctor when she lived in West Auckland, and samples were taken from stomach tissue which detected the presence of arsenic.

Pregnant Cotton gave birth to her thirteenth and final child at Durham Jail in January 1873, before she was found guilty and executed in March the same year.

She died of strangulation rather than neck breaking in a botched hanging which took three minutes. In the end, her executioner had to press down on her to speed up her death because the drop below the trap door had been too short.

The role is a change of direction for Miss Froggatt, who has been in Downton Abbey since it was first screened in 2010, and won a Golden Globe this year for the role. The last episode of Downton - a Christmas special - is being filmed now and will be finished by August.

Dark Angel is being produced by the team behind popular crime drama Line of Duty and being partly supported by Screen Yorkshire's Content Fund.