I'm in year 13, and I started this September. It's basically a project or essay on anything you want, and supposedly helps you get offers from Uni because they like it (it was one of the factors on which my UCL offer was made). I'm doing wing design and aerodynamics. Some people in my class are making movies, some are writing about blue-tongue disease, someone's researching Banksy's artwork.
It's good because I actually enjoy learning about the stuff as I research it, but you also have to do a diary of what you have done, and the research techniques you've used, which can be dull to write, and it gets more marks that the actual project itself (though my diary is full of bull****).
You have to take quite a bit of time out to research things. And you have to give a presentation on what you've done to a group of about 5 or 6 people.
I have one session a week, which is just used for general admin, and we usually get it off if the supervisor has nothing to say to us.
I started in September, and the deadline is march 19th or something.
I'm still doing my first draft of the essay, but I've completed most of the research.