I watched this documentary on the BBC's SF series, The Tripods last night and it was really entertaining, though I haven't actually seen the entire series. There are a few episodes up on Youtube that you can access however. I don't know why it was never collected on DVD, perhaps there's copyright issues or some other roadblocks. But it would be something I'd probably enjoy were it ever to see daylight again. It's taken from a trilogy of young adult novels by John Christopher.
Humanity is taken over by aliens who rule domain over us in these three-legged machines. At the age of 14 humans are forced into getting "capped", which is a alien implant and a way to erase or subdue any curiosity, rebellious ways, and make us docile to more or less worship the aliens. Three young boys (before the capping age) decide to rebel and they hear about a group of people from the White Mountain that are living with free will. They decide to leave their community and travel to be with them. That is the first season. There's only two seasons, and sadly, they didn't get to make the third, concluding season. It would be great, however, if they could make a movie from this set of books.
The above is the first part of the first episode, the other three parts on on YT as well.