Eddie Redmayne might be an Oscar winner but that did not mean it was any less terrifying joining the voice cast of the Aardman Animations film Early Man. He talks to Laura Harding about the embarrassing difficulties of working on an animated film and how Thomas The Tank Engine provided some unexpected inspiration.
Eddie Redmayne is sweaty. But please don't draw attention to it or it will make him feel even hotter.
He is having second thoughts about the chic but toasty shearling jacket (worn over a lumberjack shirt, over a white t-shirt) now he's sitting under glowing lights in a London hotel.
"I've got to the point where I'm so sweaty that I can't actually take it off," he confides.
If anyone could pull off a glistening brow though, it would be Oscar-winning Redmayne, who is as affable and charming as he is model-handsome (he appeared in a Burberry campaign with Cara Delevingne).
It might be a little surprising then to lay eyes on his character from his latest film.
The star of Fantastic Beasts And Where To Find Them, The Theory Of Everything and The Danish Girl is now voicing a toothy caveman called Dug in Aardman Animation's new movie Early Man.
The company that brought the world Wallace And Gromit, Shaun The Sheep and Chicken Run is now turning its attention to the dawn of time, when prehistoric creatures roamed the earth.
"Dug has a massive mouth, I have a massive mouth so we related there," Redmayne laughs.
"I definitely did spend a lot of my time with really wide-open eyes."
While some actors have extensive experience of voice work, lending their dulcet tones to countless animations, adverts and documentaries, Redmayne's previous experience was rather more limited.
"The only other thing I've ever done was voice the train Ryan in an episode of Thomas The Tank Engine.
"I was told they get everyone to open their eyes incredibly widely and talk with great enthusiasm.
"That is what I did back then and I took a little bit of that into Dug because he had a similar optimism."
Some of that optimism might have come in handy for the 36-year-old, who says he was a bundle of nerves about joining an Aardman project and working with famous animator Nick Park, the creator of so many beloved characters.
"I've loved Aardman since I was little but what if I went in and did the voice and they said, 'Oh, you're going to do it like that?'
"In order to preemptively not get fired, I said could we have a session where we play around with who Dug is?
"We did and sweetly Nick didn't want to fire me."
He continues: "I've known of Nick since I was growing up, watching him win Oscars, and those amazing award speeches he would give.
"He's the most affable gentleman and it's the same when you spend time with him, he's so disarming."
So how real was the fear he might get fired?
"It's happened before," he sighs. "Many a bad experience. I've been fired from many a voice-over job."
Who would fire this delightful chap? Is he joking? It's hard to tell.
"People ask you to do a film and then you stand in a booth and open your mouth and they go, 'Uh-oh, he doesn't actually have a very good voice, does he?'"
Certainly it's hard to reconcile the voice speaking now - laughing but earnest, just a trace of Eton College, where he went to school - with the slightly gormless tones of Dug.
"Normally, when you're acting you start with the script and you find who the character is.
"What is amazing here is that Nick brought in a Plasticine Dug and showed me a little bit of animation of him and he just had such wide eyes and was clearly so hopeful and uncynical and optimistic that we just started playing around there.
"We tried lots of things but it was really embarrassing - there are probably some hideously embarrassing out-takes of me trying weird and bizarre voices.
"I've blanked that memory."
Describing one particularly tricky day, he says: "There was a slightly hideous moment just before this Christmas when we were doing the last session and I had got a really brutal cold." Adopting husky tones, he concludes: "Suddenly Dug's voice (he adopts husky tones) was down here."
But one upside to the voice-over humiliations was the lack of grooming required, which must be an advantage to the father of a young child (his wife Hannah gave birth to Iris Mary in June 2016).
"You don't have to think about what costume you're wearing," he enthuses. "You can fall out of bed and arrive in the booth.
"It's probably not that pleasant for Nick if I turn up in my pyjamas, though."
But it must be strange for an actor who has gone through so many physical transformations for his roles - including his Oscar-winning portrayal of physicist Stephen Hawking in The Theory Of Everything and his Oscar-nominated depiction of transgender artist Lili Elbe in The Danish Girl - to use only his voice.
"Well, I got pretty physical in the booth," he admits.
"There is this weird thing that happens where you go to this very famous sound booth place in Soho.
"When I went for the first time I went to the loo - but the loo of this lovely place is a bit like going to a sort of slightly gross club.
"I don't know if it's the same for women, but these places have 700 different types of deodorant and eau de toilette and all this kind of stuff.
"I looked at it and I thought, 'Oh, this is a bit much'.
"After about an hour in the booth, I was spraying all of them on me.
"It's smelly, physical work being a voice-over actor!"
Early Man is released in UK cinemas on January 26.