"Correct" is an under-specified term when discussing english pronunciation.
"Received Pronunciation" (roughly, BBC English) is full of all kinds of historical mispronunciations that have become standard, often as a result of the upper classes adopting some working-class tic as a fashion. Dropping the aitch from "historical" would be an example; it was a cockney habit, adopted by posh people. It's mostly faded among folk that talk proper nowadays (at least in England; aitch-dropping seems to have survived among some groups in the US). But a lot of what's considered standard pronunciation derives from horrible mispronunciations by posh people.
[Edit] "An hotel" (with the aitch sounded) is simply incorrect; You only use "an" if you're going to drop the aitch.
My mother once heard the following sound, brayed loudly in the quad at St. John's College, Oxford: "Eh-oh, heeliaw meekyeh!" (Oh, hello Mickey). That strangled accent was common among the huntin/shootin/fishin crowd.
There was a fellow from the BBC Pronunciation Unit on the radio a couple of weeks ago, explaining (in a jokey way, as if to say it's a fuss about nothing) that "omicron" can be pronounced several ways, and that the unit had chosen OM-ee-cron. I did a term of classical greek at school; the first thing we learned was the alphabet, and we were taught to pronounce it oh-MY-cron. Classicist Mary Beard says it's oh-ME-cron, but I suspect she's inferring the way it might have been pronounced in Ancient Greece.
Boris Johnson is a classicist; I'm sure he was taught to pronounce it the same way I was. But he's using the BBC version, at least in public.
Anyhow, my confidence in the BBC Pronunciation Unit has gone down several notches this winter.