There are still a few flaws to sort out, but I've figured out how to extract KML files from Flickr groups as well as sets, how to provide either OSM or the Cycle map as a base, and how to embed the results. Results (so far) are below.
Jenkins quest set on OSM
Sustrans coast and castles set on Cycle Map
Sustrans Bristol & Bath group on Cycle Map
(Tues 12 Jan) Now slightly improved to avoid passing the KML file twice and offer alternative base map.