The pressure is on this Christmas in Casualty.

What has been described as an “emotionally epic” special, the festive episode will

see the ED team faced with an emergency blood shortage, with Stevie (Elinor Lawless)

fighting to save lives as Iain (Michael Stevenson) risks his own to ensure the hospital doesn’t go without.

“I guess the motif that runs throughout the episode is the idea of giving and the idea of sacrifice and connection,” Lawless explained to RadioTimes.com and other press ahead of the Christmas special.

She continued: “I think there’s no better place than a hospital drama to explore something like that. Our frailty and how much at the 11th hour we really depend on each other. And I think that beats really strongly throughout the episode.”

The instalment has been described by the BBC as “a tribute to the miracle of blood”, and will see the staff all face their own personal struggles as well as the events that take place on Christmas Day that push them to their limits.

Outside of the hospitals, Teddy (Milo Clarke) and Jacob (Charles Venn) are dealing with their own major incident, which Venn has described as “a very high stakes situation”, which has serious consequences for those on the ground, as they face the horror of a tunnel crash.

Venn told RadioTimes.com and other press: “At the end of the day, it’s saving lives. Of course in Jacob’s case you have a situation where we leave [and] there’s an isolated incident. One particular patient needs to be treated and then all of a sudden it turns out, down the rabbit hole if you will of this tunnel, we learn that it’s a major incident, and there are a number of casualties.”

For Jacob and Teddy, “it’s all hands on deck” in a bid to treat as many patients as possible, in what Venn has described as “a very high stakes situation”.

In addition to the chaos of the ED and the crash, the episode veers away from its usual format by featuring real-life testimonies from those who have been impacted by UK blood donation and from key workers forming part of the country’s blood service.

Venn said that he hopes the episode will serves as a reminder “of the importance of giving blood”.

He explained: “Being of African origin I am a supporter of the African Caribbean Leukaemia Trust and I discovered pretty early that the blood donation register with African Caribbeans is very, very low. It’s not high enough.”

“If it can at least raise the awareness just generally, it can save so many lives. That’s what I would ideally like the audience to take from this, just the importance of that.”