That’s not an error. It can be an affectation, but in my native southern English middle class somewhat Radio 4 accent it’s perfectly reasonable to pronounce ‘an

That’s not an error. It can be an affectation, but in my native southern English middle class somewhat Radio 4 accent it’s perfectly reasonable to pronounce ‘an historic’ basically the same as ‘unhistoric’ - or equally to pronounce ‘a historic’ with a stressed a, basically the same as ‘ahistoric’. Pronouncing it with an unstressed schwa for ‘a’ then an unstressed ‘his’ sounds awkward to my ear. And I would never drop the ‘h’. That would sound common :)