Channel 5's first original drama in eight years is a no-frills take on the police procedural. The majority of scenes were shot either on location or at a disused building in Bethnal Green serving as police headquarters.
"There were rats, it was cold... this was not glamorous!" insists Fay Ripley, who plays DI Martha Bellamy.
Shot in a stripped-back style by a documentary crew, the entire first series of Suspects came together over six weeks - 10 episodes shot mostly in sequence, with most scenes captured in one or two takes.
"There was a thing of - is this going to work out and not just look like cheap telly?" Ripley admits. "But I think it brings an interesting gritty reality to it that's somewhere between documentary and drama."
But the back-to-basics approach goes further than documentary stylings - Suspects has no traditional script, with the cast improvising their dialogue and movements based on detailed episodic scene-by-scene breakdowns. It was a prospect that Ripley and her co-stars - Damien Molony and Clare-Hope Ashitey - say they found "terrifying but thrilling".
"It was daunting to begin with because none of us had ever done anything like that before," admits Molony - who plays man of action DS Jack Weston. "I mean, I was excited but also quite nervous.
"But looking back, it's difficult to figure out a way to have done it any better. The first scene, you're in the deep end - just piling through scenes - and it's electrifying."
All three of the cast agree that they invested more of their own personalities into their characters than they might have with a traditionally-scripted drama.
"Because you don't have a rigid script, you have to base it on how you would react," explains Ashitey - passionate Detective Constable Charlie Steele. "You don't have time to think.
"I think I called someone a d**k at one point, which I really didn't mean to do! That's definitely been cut, 'cos you can't do that in an interview room!"
The show's improvised, mockumentary style "pumps in the reality" and makes for vivid, gripping television, but Ripley insists that Suspects is no threat to screenwriters: "We're making a procedural cop show accessible in a different way - we're just bringing a bit of reality to it.
"It doesn't mean that everything has to be made this way. I mean, somebody's got to write Downton Abbey - you can't improvise that!"
But for Suspects, it's an approach that works. "It's entirely in the moment," Molony concludes. "And I think that's what make it so exciting to watch."
Suspects begins Wednesday, February 12 at 10pm on Channel 5.