So in the MCU, the "Museum of Great Britain" (the MCU's British Museum I guess) has a Vibranium axe in its collection.
But in the MCU Wakanda is the most technologically advanced nation on Earth. So how would the (presumably Victorian, steam-powered) British Empire aquire the axe? Wakanda is an isolationist nation, it seems unlikely we were gifted the axe, or that they'd be willing to sell it to us. So Killmonger's statement that it was stolen seems accurate.
Did Wakanda's Industrial Revolution and subsequent rise to technological preeminence happen fairly recently and rapidly? So the British could take the axe by force in the late 1800s, but by the early 2000s the Wakandans had leapfrogged them?
That seems unlikely too. The Wakandans had the advantage of their vibranium deposits but 1) the axe is explicitly a vibranium axe, so it's not like vibranium is a recent discovery for them, and 2) they're a nation of Tony Stark-level super-geniuses, why would their Industrial Revolution be delayed until the 1900s?
Maybe they were technologically advanced, isolationist super-geniuses AND hopelessly trusting and naive before first contact with Perfidious Albion.
Maybe an unpleasant first contact with the British Empire was what prompted the Wakandan Industrial Revolution. A bit like Japan, following the Meiji Restoration.
Or maybe a courageous Victorian explorer infiltrated 1880s Wakanda to obtain Wakandan tech, so it could be shared with the rest of the world. Richard Francis Burton, maybe, he's got form. And even though they were successful, without a Stark-level super-genius to reverse-engineer the tech - alongside an unquestioning Victorian confidence in British superiority - it came to be seen as just an axe?
It would be an axe with unusual physical properties though - seems unlikely that the Royal Society would just ignore it, systemic racism or not.