Gah! You're right. I always mess that up. This is what's in my head
England = scotland, wales, ireland's hat, and the country with the guys with the fancy hats.
Britannia = just the guys with the fancy hats
UK = well I don't know.
Great Brittain = fancy hat-land plus Wales
I know it's wrong, it's a recurring mistake I make. Same with hypothesis/theory/theorem. If questioned I know it perfectly, but when it's in the middle of an unprovoked explanation I always mess it up.
Acute-term-dislexia-but-not-really-dislexia-just-some-kind-of-brainfart-thing, I believe is the medical term for it
I think silly things sometimes..