All Creatures Great and Small stars Nicholas Ralph and Rachel Shenton share behind-the-scenes secrets of the Christmas 2021 episode filmed in the Yorkshire Dales

But the chemistry test was passed, and Rachel went on to be cast in the Channel 5 adaptation as Helen Alderson, the capable, strong-minded farmer’s daughter who steals the eye and then the heart of young Scottish vet James Herriot. There have been two seasons so far, and the festive special will air on Christmas Eve, picking up from where season two ended, with the couple now engaged.

The two actors’ performances have been praised by Rosie Page and Jim Wight, children of the late All Creatures author, Thirsk “vitnary” Alf Wight, and his wife, Joan.

Nicholas says: “I can’t really tell you just how wonderful that is. Obviously, you have got the material to go off and, for me, that was the books, that’s what I focused on the most.”

Rachel adds that she had an email from Rosie Page, saying how much she liked their portrayal. “It was just so lovely to get that,” she says.

Nicholas was brought up on the outskirts of Nairn, in the north of Scotland, while Rachel is from Caverswall, a village in Staffordshire, but Yorkshire has stolen their hearts. Nicholas says: “One of my personal favourites is the little village of Arncliffe – the back of Skeldale House is what we shoot there. Now we know a few of the locals, so we stop off and have a little chat as we go. It’s all so beautiful up there.”

Rachel says: “Our series would not be possible without the support of the people in Yorkshire, particularly in the area of Grassington, which became our Darrowby. We take over that little place frequently when we are filming. Everybody thinks so fondly of the show.”

It helps that the cast and crew have become great friends. “It’s all pretence,” Rachel says with a laugh, before adding: “Yes, I really do think that contributes. We all get on very well and have done from the off, really, and hang out together off-screen. When you are creating a show that is heavily reliant on togetherness, then that absolutely does play a part.”

Filming the Christmas episode in July had its challenges, but, says Rachel, “Our designer, Jackie [Smith] does such a stellar job of creating these beautiful sets and making it feel really Christmassy. You really feel transported – and then you step outside and it’s 26 degrees.”

Nicholas had no trouble getting into the Christmas spirit. “It’s hard not to when you are dressed up as Santa Claus,” he says (yes, James dons the green suit this year).

One festive storyline features a poorly Tricki Woo and a worried Mrs Pumphrey (a brilliant performance by Patricia Hodge). Nicholas says: “It is full of love and compassion, not only for one other, but for the animals as well.

“Our on-set vet, Andy Barrett, is just superb. I always make a beeline for him any time an animal is on set. You want it to be really specific. Because ultimately you want a vet to watch and go, ‘Aye, I’ll buy that’.

“We’ll do a take and I’ll go, ‘Andy, how was that?’ and he’ll go, ‘Yeah, it’s great – you milked it a wee bit.’ It’s been a lot of fun.”

The books, Rachel points out, are packed with kindness and compassion, cleverly adapted by writer Ben Vanstone for a modern TV audience. “It could feel a bit sickly at times, if it wasn’t pitched just right, but he absolutely manages to get that every time,” she says. “The story with Tricki and Mrs Pumphrey is one of my favourites.”

All Creatures was Nicholas’s first TV role, but Rachel has appeared in several TV dramas, including Hollyoaks, and won an Oscar in 2018 for her short film The Silent Child, created and co-produced with her husband, Chris Overton, based on her own experience as the child of a parent who became deaf.

Now All Creatures Great and Small is hugely popular around the world, the jewel of Channel 5, with a third and even a fourth series said to be on the cards. Even so, neither Nicholas nor Rachel has concerns about being so closely associated with James and Helen, perhaps forever. “I still kind of pinch myself at times,” says Nicholas. “If we get to explore these characters more, which I really hope we do, it’s a blessing.”

Rachel adds: “We feel so attached to it and proud of it, and we have a sense of responsibility for telling these lovely stories.”

They continue to work on other projects. Nicholas plays the young CS Lewis in recently released film The Most Reluctant Convert, and is in The Devil’s Light, a horror-thriller out next year, while Rachel is in The Colour Room, a new British film about the life of Clarice Cliff.

Both actors are now based in London but Rachel will be heading back to the Midlands to see her mum, family and friends for Christmas, while Nicholas will head up to Scotland. “Last year, I never got home,” he says. “I had just moved to London and I missed going home, they closed the border. So this year, and every year, what I would really like to do is just be around friends and family, over-indulging and everything that you do, good food and a couple of drinks and a laugh and some games.”

Then, at some point, presumably (they cannot disclose much), they will be back in Yorkshire filming. “All Creatures aired at a time when the world felt particularly cruel and divided,” says Rachel, pondering its success. “It’s a story ultimately about community and love, and I guess that has never felt more relevant. That, as well as it’s rare now that different generations of family can sit together and watch a show.”

Nicholas says: “I think, ultimately, it comes down to that source material. It’s full of charm, wit, and humour. One minute you are laughing, the next you can be touched.

“That is one of the wonderful things about it. Because it was based on real people, and real people’s stories, there is a truth to them.”

* The All Creatures Great and Small Christmas episode airs on Channel 5 on Christmas Eve at 9pm.