In Perth-shire gentlemen only wear white tie, or at least that's what they'd have us all believe! Being a Perthie by way of Ayr-shire, who now lives in the USA after several decades sojourn in Ireland, I tend to fall into lock-step with the wishes of my host. If it says "Black Tie" on the invitation, then that's what I wear (unless the party is in Perth-shire, in which case the host should know better!).