Currently on BBC iPlayer and set to make its debut on BBC 2 this weekend, Ill Behaviour is the comedy thriller that tells the story of three friends who embark on the most testing times of their relationship, crossing all of the boundaries imaginable to save the life of one of their favourite people.

Jessica Regan is one of those leading the show – written by Peep Show’s Sam Bain – so we put some questions to her about what we should expect from the series and why she joined the show…

What can you tell us about your new series Ill Behaviour and your character Tess?

It’s a dark comedy thriller about how far you’ll go if you believe you are saving your friend from their own destruction. Loyalties, beliefs, relationships and morality are all put to the test as the characters’ course of action gets increasingly extreme.

I play Tess who is enlisted by Joel (Chris Geere) to force their friend Charlie (Tom Riley) to receive chemotherapy with the aid of rogue oncologist Nadia (Lizzy Caplan). Tess is an introvert with low confidence but surprises herself as the action unfolds. Which made her so fun to play.

Sam Bain writes the show, have you always been a fan of his work?

Absolutely. I don’t think he knows this… but when I was in second year at drama school I lived in one particularly grim place in Camberwell. We didn’t even have Freeview, we just had the five channels and box sets of Peep Show that were basically played on a loop while I lived there. It saved our brains. When I ended up being cast in an episode of Peep Show (as the actress in the play in Series 5, Episode 1, ‘Burgling’), the first person I told was my former flatmate.

What was it about the show that encouraged you to get on board?

Well, see above! If Sam Bain is involved it’s a no-brainer really. Sam initially asked me to just come along to a reading of the script telling me the parts had been cast but some of the actors were unavailable and would I be so kind, etc., as they needed to hear it out loud. Turns out Sam is a bit of a fibber, luckily for me. I loved the part of Tess so much but believing it to be gone I relaxed and had fun with it. On the strength of the reading I got an audition.

The series is pegged as a ‘comedy thriller’; how did you find balancing those two genres as part of the series?

I didn’t think about genres as such. I focused on Tess and telling her story. She made such sense to me despite the extraordinariness of her circumstances so I trusted in that and figured I’d be steered right if I went off course. You have to go for it really. If you try and end-game it and give people what you think they’re looking for it doesn’t work. Not for me any way.

Despite that comedic approach there is quite a serious underlying topic here of health and taking care of your loved ones, so which aspects of the show did you find most interesting to delve deeper into?

How far can you go when you truly believe you are doing the right thing? You’re saving a life but you are depriving someone of their choice, their agency, their humanity, even. These were knotty issues to grapple with but they’re the kind of stories I’m interested in telling.

What was the chemistry like with your co-stars on the set of the series?

I had a ton of fun on set. The cast were terrific but so were our crew. I felt the least cast/crew divide on this job than any other. We hung out, went to the pub together… it’s not always like that and I love that atmosphere. I was quite intimidated coming onto this show having the least experience of the main cast, but Chris Geere minded me beautifully, particularly during some of the more demented moments of the shoot.

Steve Bendelack directed the show; how was he to work with?

I think the director Stephen Bendelack did a brilliant job of guiding us tonally. It could feel a bit alien at times but I’m so glad I trusted the process. No tricks on his watch! He had such a strong sense of the world of these characters. He could totally see the wood for the trees which could be hard for the actor at times. He’s a true collaborator and encouraged me to be inventive and playful.

The show has been made available on iPlayer ahead of its BBC 2 debut; what sort of response have you had to it so far?

The response has been great! People seem to have just strapped in and come along with us on this dark and twisty tale. I understand it can be a hard watch at times but so far, it’s been overwhelmingly positive.

Aside from the show making its debut on BBC 2, what else should we expect from you in the coming months?

I’m starring in an Irish sitcom called Nowhere Fast that will air on RTE in October and is being distributed by BBC Worldwide. It’s written by and starring Alison Spittle who is a serious name to watch…

Ill Behaviour begins on BBC 2 on August 20 at 10pm.