Sister Julienne star Jenny Agutter said: “When we we amongst those standing stones, you could hardly see in front of your own face.
“And then I couldn’t hear Miriam, we were sort of looking at one another to see if the mouths were moving and it was so wet.”
Meanwhile, show runner Heidi Thomas, confessed she was worried she would be visited by Lady Sophie Scott, who haunted the place they were staying in.
Helen revealed to Metro.co.uk: “I used to come downstairs each morning wondering whose body was going to be discovered in the drawing-room.”
Call The Midwife Christmas Special airs tonight on BBC One at 7pm.