Herman Miller armshells in UK/Europe?  

I am located in the UK and sometime around the early 2000's (or maybe the late 90's, I remember it was around the time when 4-wheeled chairs were made illegal in UK workplaces) I picked up a pair of Herman Miller upholstered armshell chairs from a second hand store. They are finished with a lovely Alexander Girard fabric in blue, the shell is white or off white, the base is aluminium with casters and the date stamp is 1976. I am sitting on one of them as I write this, I use one of them every day as a desk chair and I absolutely love sitting in them.
My question is: Why are Herman Miller chairs here?
I always thought that Eames/Herman Miller licensed the European production of these chairs to Vitra? When did this relationship start? Were the chairs manufactured by Herman Miller ever sold in the UK?