Probably the closest to home entry the website will ever see. I found this whist digging the garden a few months ago and have gradually cleaned it from a blob of rust into a recognisable button.
After a little investigation I believe it to World War 1 General Service Corps button,
Heres a mint example from Cold War Warrior
I was metal detecting in my back garden and also found a button identical to yours. I have no idea where it came from though.
I recently got several of these buttons. I’m finding it hard on trying to find out more about the general service corps.