Cast announced for BBC One's Call the Midwife: Sisters in Arms

As filming begins on a three-part Christmas special.

BBC One has announced that filming has begun on a three-part Christmas special for Call the Midwife's prequel series, Call the Midwife: Sisters in Arms, which is created by Heidi Thomas and is set in Poplar during World War Two.

The series features some well-known Call the Midwife characters as their younger selves and is narrated, as the older Sister Julienne, by Jenny Agutter.

In September 1939, Sister Monica Joan is in her prime, Sister Julienne and Sister Evangelina are young and zealous, and Nonnatus House is the beating heart of Poplar. Together with Sister Alice, and local GP Dr Kit, the nuns dedicate their lives to mothers, babies and the poor. But there is no gas and air, no penicillin, no cure for TB, and no welfare state. Then war is declared, and life gets even harder.

The three young secular midwives who complete the team, Sybil, Olive and Marianne, receive a baptism of fire as the blackout and the Blitz take hold. While bombs rain from the sky, women give birth underground, families are shattered, children run wild, and whole streets are reduced to rubble. But courage, compassion and resilience triumph as the community unites in its efforts to survive.

Julie Hesmondhalgh will guest star as Sister Alice, with Martin McCann guest starring as Tommy Moffat alongside Rachel O'Connell as his wife Mary.

Sister Evangelina will be played by Amy Booth-Steel, alongside Helen Schlesinger as Sister Monica Joan, Helena Wilson as Sister Julienne, Bally Gill will play Dr Kit Malhotra, Liv Andrusier will play Marianne Siegler, Lizzie Back will play Sybil Maxted and Ellie Mckay will play Olive Dobbs.

Elsewhere Ciaran Bowling will play Fred Buckle alongside Ami Metcalf as his wife Betty, with Ben Rose as Dr Patrick Turner.

Speaking ahead of Call the Midwife: Sisters in Arms, creator and writer Heidi Thomas OBE said "Having loved and lived with the Sisters of Nonnatus House for so many years, I found myself longing to turn the clock back and tell the story of their finest hour - the Blitz. Who were Sister Monica Joan, Sister Julienne, and Sister Evangelina, when they were young? What did they do, how did they survive, and how did the conflict change them?"

"Above all else, Call the Midwife: Sisters in Arms is about what happens when women go to war. It is about love and birth, separation and courage, lipstick and nylons (or the lack thereof). But it is also a medical drama, set in a devastating landscape where even the nurses cannot know if they will live till morning."

"I thought I had cried all my tears when Sister Monica Joan died, at the end of Call the Midwife’s 15th series. But the thought of her back on her bike, cycling through an air raid, set me off again, as did images of young Sister Julienne shaking when the sirens sound, and Fred Buckle still in his 20s, black with soot and sweat as a volunteer fireman. Then I'd be laughing at Sister Evangelina, in her element as an Air Raid Warden, or the juvenile Dr Turner turning up at a dance and being shy with girls."

"Sisters in Arms has been a joy to write - like returning to the family home and finding all the people I have ever loved made young again and filled with new energy. I can't wait to start filming and look forward to sharing our new show with Call the Midwife’s fantastic fans."

To which executive producer Dame Pippa Harris DBE, added "It’s thrilling to watch Heidi Thomas create a series which I know will delight our loyal Call the Midwife audience, as well as drawing in new viewers. It echoes the original through its blend of engrossing medical stories, wit, and pathos, while the backdrop of WW2 adds a completely fresh layer of tension and jeopardy to the drama. Heidi’s extraordinary skill with character and story means viewers are in for a real treat this Christmas."

And the BBC's Director of Drama, Lindsay Salt, said "We feel immensely proud to continue our partnership with the Call the Midwife team to take this very special, much-loved series in such an exciting direction. The cast assembled for Sisters in Arms are every bit as wonderful as Heidi’s scripts, and we can’t wait to take BBC viewers to the Poplar of 1939 to get to know them."

Made by All3Media’s Neal Street, Call the Midwife: Sisters in Arms is created, written and executive produced by Heidi Thomas, and executive produced by Pippa Harris and Ann Tricklebank, who also serves as producer.

Ann Tricklebank will direct episodes one and two, with John Maidens directing episode three. Jo McClellan is the executive producer for the BBC.

Further details about a full-length Call the Midwife: Sisters in Arms series will be announced in due course.

Call the Midwife: Sisters in Arms will air on BBC One