If you're looking for a documentary, then Documentary Heaven would be a good place to start. I've said that it has thousands of free documentaries, but in truth I don't have a specific number since they don't tell us. However, there are an awful lot of them! There are about 50 different categories, from Activist to War, with plenty of different subjects in between. The search engine is ok, but it's not brilliant, and I found it was best to simply browse through a category.
Content comes from a variety of places - Documentary Heaven doesn't host the content itself, that comes from Google Videos, YouTube, Vimeo and so on. Documentaries vary in length from a few minutes up to an hour or more, and they are from various countries - I found several from the UK in my brief searching. Because they don't host, videos were of variable quality - some were really clear, others were quite pixilated, and the sound was loud, or really quiet and so on. I also didn't like the fact that with one or two you got taken to another site and had to register before viewing a documentary, and I was wondering what on earth was going on.
However, those niggles apart, it gives you access to a lot of documentaries completely free of charge, so it's worth keeping this one in your locker in case you ever need one!