How LEE filters are made

Like a great many photographers I am using LEE filters on my flashes and lenses.
The 200+ sample pack has pretty much become a standard item for strobists.
What I just watched is a video about how they are made.
I'd never have expected this to be a 2.5 day purely manual process done in the UK.
My guess would be some kind of highly automated manufacturing plant somewhere in asia.
You don't see much of that kind of manual work anymore.