My own theory (as yet unproven) is that they pop up in the UK so frequently and in many different (and generally non-Holmegaard) colours because production of some of them was outsourced to a UK company at some point in the 1960s/70s, much as they did with Cascade Glass for the 'Gulvvase'...
I should probably keep my mouth shut in public forums when broadly speculating - I've just spotted an eBay auction for a Cascade moneybox that mentions in the text that Cascade also made moneyboxes for Holmegaard - clearly an idea taken from here and presented as fact. Incredibly frustrating!
Trouble is, speculative posts sometimes
do lead to interesting places - after all, it was mention of Gulvvases with Cascade labels on here by Adam P that lead me to hunt out their background. But is it worth it if they (the ideas) are just going to get twisted out of context in the meanwhile?