Complex sentence: Prior to the founding of the Delphi Heron Books, there was a London publisher called Heron Books which published faux-leather classic books in the late 1960s and early 1970s.
Split into simpler sentences: Prior to the founding of the Delphi Heron Books, there existed a London publisher also called Heron Books. It published faux-leather classic books in the late 1960s and early 1970s.