Why did he have an aussie accent in the film when he should have had a devonian one? Mind you, my dad is from Devon and he does say ‘strewth’ alot, so maybe they’re pretty kindred...
He didn't. Woodward used his natural RP accent.
We don't actually know for certain who Morant was. There's two competing versions. Personally I lean towards the Somerset origin rather than the Devonian one. But as to what his voice really sounded like, I'm not sure what accent he had. Australian accents have altered substantially even in my lifetime and depending on social class and background can differ a lot. I'm Australian born, but a lot of people assume I'm English when they meet me for the first time, because I've got what would probably be described as an "Upper class Victorian/South Australian accent" which is what I was raised as from the age of 9 or so.