Airing this Saturday (10th December), the episode breaks from Casualty’s traditional scripted format.
It'll focus on paramedics Jan, Iain, Sah and Teddy, who are pushed to breaking point whilst working under pressure.
The episode follows the paramedics across four days and shows the pressure and obstacles they are faced with on busy shifts. Jan, played by Di Botcher, arrives back from holiday with a spring in her step, but is ground down over the course of her shift and makes a terrible mistake, resulting in an accident.
Played by Milo Clarke, Teddy's confidence is undermined on a difficult call out, and Iain, played by Michael Stevenson and Sah, played by Arin Smethurst, both battle with intensely stressful situations.
Casualty is the world’s longest running primetime medical drama and over the show's 36-year history, it has a had a proud tradition of reflecting the difficult realities front-line health care workers are faced with, and this episode continues that tradition as it sheds light on the effect ambulance queues has on the hospital, its patients, and the front-line medical staff themselves.
Speaking about the show's first ever improvised episode, Casualty's Executive Producer for BBC Studios, Jon Sen, said "Casualty is at its best when it tells stories that truly chime with the real experience of working medics in the NHS."
"The ambition behind the ep was to tell a story that gets as close as possible to what it is like to stand in the shoes of paramedics up and down the country. After our extensive research, using improvisation techniques to capture the truth of the world seemed only natural. We want people to come away having a greater respect for the work paramedics do and a true appreciation of the challenges they face."
The episode was directed by Steve Hughes, who added "The actors improvised all their dialogue and we shot everything like a documentary to give it a grounded, naturalistic feel. It was vital to make this episode feel as authentic as possible to highlight the challenges paramedics, and the NHS as a whole, face on a daily basis."
"It was scary for the actors at first, like they were walking a tightrope without a net, but it was also freeing and exciting to be able to use their own voices and, even though most of them hadn’t done anything like this before, they all rose to the challenge and I’m so proud of what we achieved."
Casualty returns Saturday 10th December at 8.10pm on BBC One