Quatermass, by Nigel Kneale:

Back in 1979, I was a horror and science fiction hungry pre-teenager when I saw the serialized adaptation of this book on TV. The series (back in its day) was great. I haven’t seen it since and I can guess at just how dated it would be now on a second viewing. However, it stayed with me over the years and inspired me to read the source novel. This is a very different and absorbing “alien invasion” story in that we never see the aliens. Instead, as society crumbles, fuel and food shortages have driven the populations to desperation and violence, anarchy reigns on the urban streets in a nightmarish near-future, the young people around the planet have become like hippy, new-age wanderers. Calling themselves the Planet People, they are being hypnotically lured to various locations where they are “harvested” on mass, leaving only the old behind to face extinction. Are the Planet People, as they believe, being magically transported to a heavenly other-world, or is a malevolent alien race blasting the planet surface with a laser and slaughtering them? Professor Quatermass sets out in a race against time to save both his missing granddaughter and the rest of mankind from annihilation. You’ll never look at a stone circle structure such as Stonehenge or a hippy the same way again!