What is the etymology of these non-words?

uh
inarticulate sound, attested from c. 1600; uh-huh, spoken affirmative (often ironic or non-committal) is recorded by 1894; negative uh-uh is attested from 1924. That’s from the Online Etymological Dictionary.

^Do you use these in British English?

Yes, we do. It isn’t just American English.

Thanks for that correction.

We’ve got some dates, but no information about the origin.

Yes, that would have been helpful. Maybe that information is in the printed version.

Found this on a Quora thread which is a little help:

Is the meaning of “mmhmm” and “uh uh” universal?
Filler words like that, more technically discourse markers, which allow us to gather our thoughts, pace our utterances, and add emphasis, are likely universal[1]. But the specific sounds in English aren’t used the same in all languages[2]. At the same time, these tend to be very basic sounds (easy to pronounce, simple forms) that might be relatively widespread because of that[3].

@janbb Thank you. Very helpful.