"order a helmet" - Why not "an"? [duplicate]

I've encountered the following sentence:

order a helmet

Shouldn't it be "order an helmet" instead?

As a first approximation, "an" would be used if the initial "h" wasn't pronounced, as some variants of English do with "herb". In "helmet" the "h" is pronounced in most accents, so we use "a".

Of course being English it's never quite that simple - in "an hotel", which used to be common, the "h" is often clear. That has been known to apply to "herb" in British English too.

If, like me, you're from London (UK), you say be prone to dropping the "h". So speaking formally, I'd say "a helmet", but informally might say something more like "a nelmet"