The Three-part Episode Is a Prequel to the Series, Set in Poplar, East London, in September 1939 During the Outbreak of the Second World War

First-look images have been released for the Call The Midwife Christmas special, Sisters In Arms, as filming wraps. The three-part episode is a prequel to the BBC series, set in Poplar, east London, in September 1939 during the outbreak of the Second World War. The pictures show new cast members Julie Hesmondhalgh, Helena Wilson, Ellie McKay, Liv Andrusier, and Lizzie Back in their uniforms for the first time.

Writer and showrunner Heidi Thomas said: "Call The Midwife has a long and noble history of filming Christmas specials during heatwaves, and this year we welcomed the snow-machine back to the Nonnatus House set like an old friend. But I was surprised how many new emotions Call The Midwife: Sisters In Arms sparked. In particular, the evacuation of Poplar's children, and the fear that they may not make it home for Christmas had us all in tears.

The series, which follows nurse midwives in east London through the decades, began in January 2012 and has had 15 series, each with a Christmas special. A BBC synopsis reads: "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 those in need.

But there is no gas and air, no penicillin, no cure for TB, and no welfare state. 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. An exact broadcast date has yet to be announced, but the special will air during the festive period. Previous series are available on BBC iPlayer.