Hmm.. well I couldn't really let this pass without comment! It's a shame they found that missing blade right below the turbine, otherwise this would have been pretty baffling!
I do quite like the Daily Mail theory about the unmanned aircraft, Taranis, being tested along that coastal stretch, but unfortunately, according to the Telegraph:
"The MoD has denied earlier reports that any testing of new Taranis unmanned stealth aircraft was taking place and confirmed that the nearby Donna Nook test range was closed to any low flying aircraft over Christmas until the January 6. Taranis is not due to begin testing until 2010. The Civil Aviation Authority also confirmed that they had not granted any permission for the flight of unmanned aircraft, which are banned in UK airspace without special arrangement. "I've had a little look on YouTube, and it's amazing to see the amount of damage a wind turbine can do to itself (see video). The only problem with this theory that I can see, is that maybe the Conisholme turbine remained a little too intact!