Harry came home! Apparently he was lurking in a neighbour's empty flat, and when the people who look after it opened the door, he shot out. I am now seriously considering fitting him with some sort of remote tracking device. I am hugely hugely relieved, and so is Nick.
I've phoned round all the people I phoned to report him missing to tell them he has been found, and Nick has gone out to take down the posters.