All the fun of the fair?

I was bicycling to work along the south side of Hyde Park, admiring the last of the autumn colours, when, glancing to my left, I saw an enormous Ferris wheel. I know I am strictly a fair-weather cyclist and this week has been a rain-filled one, but this huge machine has sprung up near Hyde Park Corner without anyone — all right, me — knowing anything about it. Who put it up? When will it start working? How long is it there for?