New sprocket fitted to the hub. Didn't spend time cleaning the wheel up much, as it was 10:30 pm when I'd reached this state of affairs, and took this one and only photo for the day. Then it was out to the garage fit the wheel, and a new chain, and set up the brakes. One slight hiccup, which I eventually figured out and sorted. So I should be cycling to work tomorrow. Really should sort at least one of the other suitable commuting steeds - it's good to have a backup, and they're a darn sight easier on the wallet than crazy car bills...