King George Butterfly

I grew up in Bedford, but have lived in SW Cumbria for the last 40 years. Last week, while doing a butterfly count, I bumped into my (local) hairdresser who commented that she’d had a lot of “King George” butterflies in the house. I worked out that she was referring to the Small Tortoiseshell and assume that it must be a local name, although my husband, who is a local man, has never heard it.
I’ve tried Googling the name, and ten pages just give four results. One a photo taken in Whitehaven, a book by a man who grew up in Yorkshire where the name was widely used, and two blogs asking about the origin with suggestions that it is a northern name.
I am curious to find out why the name King George should be attributed to this butterfly, and why in the north. Does anyone have any ideas?

I am in East Anglia and have never, ever heard it called that…