It's referred to as a white tie event in the main promotional blurb, RoxySiren, but as a black tie one when you follow the ticketing links.
Rather embarrassing if, £200 later, one turned up sporting the wrong evening wear, old chap!
Still, at least it'll stop MCC members from wearing their yellow & orange (fried egg & tomato) striped ties; I fear BF & the band would otherwise have needed sunglasses...
Wonder how long a set they'll get for £200? 45 mins or an hour maybe?