Born in Oxford, Lawtey had to put on a Welsh accent and learn some Welsh.
"We start the film with this strong Port Talbot accent and some Welsh language too, and over the course of the film he has to uncover this RP (received pronunciation) voice, we call it in the business, which is quite a well-spoken, proper, quite Anglified accent, really, that we've kind of come to recognise in Richard with those hints of Welshness in there as well," he said.
On learning to speak some Welsh lines, Lawtey said he felt almost "embarrassed" but had support from the Welsh speaking writer, producer and director.
"Those are the ones that were giving me recordings that I could follow and kind of try to hone as best as I could," he said.
"You know, it really mattered to me, deeply, more than anything else, that aspect of the film felt as authentic and true and respected as possible, because it's so significant in Richard's story and his life."
Bafta-winning actor Toby Jones plays Burton's teacher who discovered his talent for acting.
Lawtey said filming alongside Jones in Burton's home village of Pontrhydyfen was like a life-imitating-art experience.
"This film is a story of mentorship, I suppose, and if you speak to any actor worth their salt, they'll have had many people over their careers who kind of given them something of themselves and kind of push them on their way. And Toby certainly represents that for me."