I think, like most manufacturers, there's hotspots around their location and it gets thinner the further out you go.
I see plenty but I play in Leicestershire, and up until this season had been playing in Derbyshire. And Nottinghamshire before that. Therefore, I also see a lot of Aldred and some Charlie French.
But when I played a few seasons in East Anglia I don't remember seeing as many (could be my memory though), but did see a lot of Warsop and yet haven't seen any Warsop in the East Midlands since. Appreciate Warsop is on another level to GM, but just an example.
It's one of the biggest benefits of this site to be honest, being made aware of brands outside of what I am normally exposed to.