"Aitch" is definitely still very much in use in UK - among older people, particularly.
And I would (indeed, do!) certainly both talk and write about, "an historical treatise," for instance.
I would also say, "an hallucination;" to use "a" would sound wrong to me. But "a hunk of meat" is the only possibility, I think, or "a hopper."

It Begins to look as though, for me at least, if the second letter of the word is "a" or "i", then I would usually use "an "; if it is "o" or "u" then and "a "


(But it would "a hive of bees" I guess!!!!



signed confused, of UK