Rochenda Sandall had a "special, girlie-shaped" balaclava for Line of Duty series five

Speaking in the new issue of Radio Times, the actress – who plays balaclava gang criminal Lisa McQueen in the new series of Jed Mercurio's beloved cop drama – also explains the costume department's difficulties in sourcing the woollen face masks in Northern Ireland, where the show is filmed.

"All the headgear had to be bought in and brought out from London, as there are restrictions on the sale and wearing of balaclavas in Belfast due to the history of their use by terrorists."

• When is Line of Duty back on TV?
• Line of Duty spoiler-free review: a triumphant return – with a menacing new villain and plenty of twists and turns
• Line of Duty stars “panic” when they get the scripts – in case they’ve been killed off

And while they look like they might cause the actors to overheat, she assures us that body temperature was not an issue in midwinter Blighty when Line of Duty was shot.

"They probably would [get too hot] in the middle of August," she says, " but we were filming in winter, a lot of it at night, so I was often glad of the balaclava."

Sandall joins returning AC-12 officers Kate Fleming (Vicky McClure), Steve Arnott (Martin Compston) and Ted Hastings (Adrian Dunbar), and newcomer Stephen Graham, who will play her literal partner-in-crime John Corbett, the apparent head of the balaclava gang that have been in or around the action since the show's beginning.

• From Tony Gates to Roz Huntley: how are the first four series of Line of Duty linked together?

She is tight-lipped about her character's arc over the course of the series – if previous runs are anything to go by, she'll do well to make it to episode three – but she does air her relief at not having to get versed on "police jargon" like her co-stars.

"Most of my scenes are dialogue with Stephen Graham, which is shorter [than the traditional interrogation scenes]. And our big luck is that we don't have to learn all the police jargon, which is the big problem for Adrian, Vicky and Martin because they are having to learn jargon that they wouldn't naturally know."

You can read a full interview with Rochenda Sandall and co-star Stephen Graham in this week's edition of Radio Times, available in shops and on the newsstand from Tuesday 26th March