TWO years after gripping viewers, Line Of Duty makes a welcome return to BBC2. For those needing a reminder, the first series introduced straightarrow anti-corruption cop Steve Arnott and his colleagues, who were investigating the possible crimes and misdemeanours carried out by DCI Tony Gates.

Martin Compston, Vicky McClure and Adrian Dunbar are among those back on duty, while Call the Midwife’s Jessica Raine joins the cast as a rookie detective constable.

Sadly Lennie James, who played Gates, isn’t in this series because Arnott and his team will be tackling an investigation into a different case of suspected police corruption.

Series writer and creator Jed Mercurio says of the focus of the series’ investigation: “I wanted to create a character as far from Tony Gates as possible. “Detective Inspector Lindsay Denton appears to be a mild-mannered, backroom detective – and her social and professional isolation make her a figure of mistrust. Playing against type, Keeley Hawes is an absolute revelation.”

Denton is the sole survivor of a police convoy ambushed while escorting a protected witness. Arnott immediately suspects she tipped the perpetrators off, but proving it may be difficult.

“At first when I went and met Jed and Douglas, the director, they weren’t too sure whether Lindsay would be on the dark side or not, which was so fascinating for me,” says Hawes.

“I was sent the scripts and I just sat there and read them one after another in one sitting.

I still had no idea and I begged them to tell me – regardless of whether I got the part, I just needed to know.

“They told me that they hadn’t decided so it was quite incredible to go in and play the scenes completely not knowing whether I was guilty or otherwise. I’ve never had to do anything like this before.” There was one aspect of playing Denton that Hawes was not so enthusiastic about.

“I didn’t love going into the make-up truck every day and having them look at me saying ‘yep, that’s great.’ without even brushing my hair, actually only putting a bit more dark under my eyes,” she says.

“But it’s quite liberating once you get used to not even bothering to wash your hair and people just adding a bit more grease. It’s liberating for me as I have played lots of glamorous characters and this is the absolute opposite.”