Aha, found the answer to the Beacon Hill question, thanks to www.thorneycroft.com. Apparently it's named after one or more Beacon Hills in Wiltshire, as a Wiltshire landowner, Thomas Poynder, owned the land in Holloway on which this and other streets were built on the 1870s. So in a way, it is named for the ancient beacon fires lit by prehistoric colemen, just not in that actual place.