There may be snow on the ground in the Call the Midwife Christmas special, but cast and crew filmed scenes at the Historic Dockyard Chatham back in May.

Here, Jenny Agutter, who plays Sister Julienne, talks about filming and the ever-popular show.

This year’s festive special covers the big freeze of 1962 – how did you find filming?

It was wonderful. We had all the icicles, we had snow around - it really looks amazing. It’s not easy to do because it’s a big production – there was a lot of work around the snow. Also, it’s blindingly white, so if the sun comes out you can’t really see.

Do you have memories of the big freeze yourself?

I was living in Cyprus, and I came over to boarding school at that time. I remember this icicle hanging off the roof, and having to wear all the clothes one possibly could because there was no way they could make the school warm.

You shot the festive scenes in May at Chatham Historic Dockyard – how was that?

We like to do everything completely out of order! So, we did have a bit of sunshine - but it looks lovely. And actually, part of the reason it stayed frozen was because the skies were quite clear. If it was heavy and cloudy, it [the snow] would have been melting.

What do we see the midwives dealing with in the Christmas episode?

We’ve got a pretty heavy-hitting story, because [historic] child abuse comes into it. But all of our Christmas episodes have had quite difficult things in them. The difficulty with this is that something like [historic] child abuse leaves such a lot behind it; you can’t repair that damage. You can just show a community that supports somebody. But it is a shocking story to read.

Do you find it hard not to take the difficult story lines home with you?

I work anyway with Action For Children; mainly projects that are to do with youth homelessness, but they deal a lot with abuse, whether it’s sexual abuse or physical abuse. Most young people end up on the street, not because it seems like a more romantic life, but because they’re running away from something ghastly. So, when I get a story like this, it actually deeply affects me, because it rings true.

Why do you think Call the Midwife remains so popular?

There’s always the possibility of a better future when a child is born. Unless they’re born into terrible circumstances - but you’re always hoping that that child will have a better world, a better place, a better life. And they bring huge hope, it’s just gorgeous. That, plus the fact we are moving through time. Young people look at it as very much a period piece, older people look at it and remember the times.

Series 7 starts next year. Can we expect new cast members?

We’ve got Lucille [the first West Indian midwife to feature as a regular character, portrayed by Leonie Elliott] arriving in episode one, which is lovely. Although we’ve had many people in the community from different places, we haven’t actually had someone that we’ve employed. But, of course, that time is absolutely right, because they were bringing a lot of people over from the Commonwealth to join medical services. And that has thankfully continued.

We know there will be at least three more series so what will it cover next?

The exponential changes in science and the arts, and then into society, were enormous in the 1960s. All that stuff that had been held back in the War, was really starting to burst out. As we get further into the 1960s, one will really see the effect of those changes in Poplar. So it’s quite exciting!

Call the Midwife is on BBC1 on Christmas Day at 7.40pm