Thanks to Nick I have managed to get the cover_url part of my objective working. As per Nick's very reasonable request I have been messing around with recipes and reading documentation as best I can. I have spent all of yesterday evening also trying to get the metadata to automatically be seeded with the author set to something like "The Independent". So far I have been wholly unsuccessful.
I have tried
author = 'The Independent'
authors = 'The Independent'
author_sort = 'The Independent'
None of these seem to modify the metadata during download and I am still left with the author of all the feeds set to calibre.
Thanks for any help and suggestions.