Yeah, the two guys in England can't possibly being doing the circles that have appeared in other countries. I saw a special on either TLC or Discovery that said back in the mid-80s and early 90s, an average of 3 crop circles were formed each night worldwide.
I think a lot of the circles are hoaxes, especially the ones in later years. But originally, there was another cause which inspired the hoaxers.
The same special had video of two occasions when a crop circle was formed by balls of light -- possibly plasma balls. One video, after analysis, looked like it might be a fake. The other one seemed to be legit.
They also interviewed an older man who said that, as a young boy during World War II, he saw a crop circle form in a field right before his eyes, and his description of what happened supports the plasma ball theory as well.