I have never heard maître used in the UK, even at fancy restaurants (though I have never been anywhere really fancy)!

We never use "maitre" alone. We use both "head waiter" and "maitre d" (short for maitre d'hotel). We usually don't add the circonflex accent.

In the US I think "maître d" (may-truh-dee or may-ter-dee) is just as common as "head waiter" which is not too common.

Thank you Peter!

It depends on the restuarant. Some restaurants (especially in the UK) may use many French terms. France has more of a cooking culture than the UK so many terms are borrowed. It could be seen as trendy to do it too.