Birthistle joins the cast in Series 9 Episode 1 as a new regular character, Detective Superintendent Sarah Cavendish.

Johnson, who has played Detective Inspector Spencer Jordan since the show started in 2000, told BBC Press Office: “Having two Detective Superintendents is just not the norm; it’s not how it works. But she is vital, she is good at her job and Spencer respects that and because she comes from another unit she brings something else to the table, which is useful – she’s not just occupying space.”

He continued: “Sarah has an incident with a gun in Episode 1 where she goes a bit overboard and we’re saying, ‘Hang on a minute, steady!’ It was a bit shocking for us because we can get a bit heavy-handed and we do what we need to do when necessary but for those circumstances it was completely overboard.”

He added: “As the series progresses it reveals itself, that there is real trauma in her life.”

Series 9 begins at 9pm on Sunday 13th March.