Velvet slippers, known in England as Alberts after the prince who made them famous, were not all that easy to get not all that long ago. If a man was unwilling to bespeak a pair, few places had them available off the shelf and what could be found was pricey. The dark green Edward Green's in the photo were made to order rather than bespoke and I believe they were $600 at the time even so.
Of course, velvet slippers were perhaps worth that kind of money. Warm, fairly comfortable, personalized with virtually any kind of symbol or monogram and built for wear on the stone floors of unheated castles so they last much of a lifetime, an eccentric or a dandy could always bring them out for his driving trip across Africa a la Bob Geldof (see Rats, Boomtown). The less adventurous could be seen slipping them on in the first class cabins of trans-Atlantic flights. And lately some guys are even wearing them on first dates.
Fortunately, more than one firm has seen opportunity in Alberts, and they are easier to come by these days as well as less expensive. Stubbs & Wootton, for example, have built a minor empire selling them to American men and women for $395 (£250) a pair. And Del Toro Shoes, a newer company in the U.S., has them for $195 (£125). How times have changed.
These are not all identical from maker to maker of course. Those Edward Greens are considerably heavier and have thicker soles than the Del Toros. Still, the two are virtually indistinguishable from a few feet away. And that is a good thing.