Despite the smallish fee on offer, Robbie Williams was only too happy to co-write and sing the song featured as he was a huge fan of Raymond Briggs 'The Snowman' animated short film of the mid 1980s as a child and wanted to be part of something equally magical that children would still be watching at Christmas decades later. And despite being a major Hollywood film and television star, Benedict Cumberbatch's involvement was also because of his fond childhood memories of The Snowman.
The book was published 51 years before the first broadcast of this film. Although the book was always popular amongst small children, it was rediscovered when adapted for a children's stage play in the early 2000s. The play was hugely popular and has been ever since. This resurgence in both the story and its author is what prompted the producers interest in making this film. Judith Kerr agreed only only if she had a say in the voice casting and animation style.
David Walliams has been involved in children's animation before as a writer and voice artist. However he credits Judith Kerr with introducing him as a child to his eccentric style. He was delighted to be involved and his participation ensured the project would be treated with respect, much to Judith Kerr's relief.
Author Judith Kerr died before production was completed. It is unknown if she saw a rough cut of the film.