The Taken actor stars in the emotional tale about a young boy (Lewis MacDougall) who is struggling to come to terms with his mother’s (Felicity Jones) cancer diagnosis. Liam voices the title yew tree monster and went to great lengths to bring the magical creature to life on set.

Talking to UPI (United Press International) at a roundtable interview in New York, Liam explained how he had to pretend he was 40ft tall and every move he made was documented by 70 cameras.

"And you're in the middle," he recalled. "And you're in a onesie with ping-pong balls attached to you. It's totally ridiculous. And they're all connected to sensors and the computer nerds are giving you digital make-up is what I would call it. And you're acting away."

Liam shares a lot of scenes with his young co-star Lewis, however the pair was not in the same room during production. The 64-year-old had to act opposite a puppet or small doll in order to keep proportions in place, and it was an experience Liam found "interesting".

When it came to perfecting the vocals of the monster Liam carefully analysed the facial features of his alter ego via a statue of the character, noting how its appearance would affect his vocals.

"That informed me a lot because it looked like someone had just squashed their face up against a tree," he explained. "And I thought, 'Well, his nose is broken, so that affects breathing and that'll affect the voice in some way.' And just those little things.”

The Love Actually star describes the tale, based on Patrick Ness’ novel of the same name, as "very entertaining and emotional". Also starring Sigourney Weaver, J.A. Bayona's A Monster Calls began hitting cinemas in October (16).