Bitcoins are digital money ‘mined’ from satanically difficult mathematical problems. Madness, obviously. But five years ago, while the rest of us were saying ‘Huh. Geeks. Money in cyberspace’, or ‘Y’what?’ a young doctor I know bought a few quids’ worth for fun. Sold it later for £800. Now she’s out on a hillside in the driving rain with her hawk.