See, yesterday wechsler's disappeared, and he's had to borrow one of mine (grey with an orange interior).
I stood up to exit a train today and my favorite black wool hat leapt off of my lap in a subtle manner that nearly resulted in my leaving it behind me, on the floor.
In the meantime, I found not one but two black hats today. One of them was hanging on a gate post and the other was leaning against a wall. They were both a bit damp.
So if you own a black hat and live in London, keep an eye out. I'm not sure if they're just getting together for a convention or trying to go all the way to Vegas, but it does seem that there's a great movement going on and you're likely to see yours depart at any moment. On the other hand, they move slowly and can be fairly easy to catch, so it's possible you may find one that has tried to sneak off unsuccessfully in the next few days and can return it to the fold of civilization without a fight.