Can't remember much about this. Was it sort of post-apocalyptic. And didn't something strange happen everytime the heroine went under an electricity pylon? Isn't it something to do with this noise which starts, and it makes everyone go mad and stop using/start smashing electrical machines, and you get the kind of apocalypse only Britain could produce, and it's all pastoral and muddy, and then the kids sort it out (presumably so they can play Mario again)? Based on a Peter Dickinson series of novellas.