“Oxford” and “British subject” are but names in a game of British Empire PR

In the same regard Scotland could claim significantly more inventions on the basis of many English inventors who lived or worked in Scotland or at Scottish universities

To follow your logic back to my original assertion

Without Fleming = no penicillin

What you need to consider is probability

There is a higher probability of something already discovered being advanced by someone else than the probability of the initial discovery

Flemings accidental discovery and crucially his recognition of this discovery as something worth noting despite at the time having no practical application is an improbable chain of events than cannot be easily repeated - accidental discoveries still require intelligent recognition by the person who discovered them to ensure they are not simply lost

For example the probability of someone else discovering what, say James Clerk Maxwell discovered is low