Hi Gareth,
Thank you for the beta version of Collapsed Topics for Moodle 2.3. I installed your course format, set the course layout to "Show one section per page" and and selected "Collapsed Topics format" with current topic at the top, no cookies, and no toggle word, toggle section x and section number.
These are the first three sections of the main page.

This is the view of section 1. (see below)

This is the main course page in editing off mode. (see below)

This is section one in editing off mode. (see below)

"Show one section per page" may not be compatible with Collapsed Topics format as all activities and resources disappear as well as "Add an activity or resource" when only one section is selected.
Another observation: Is it possible to change once mind regarding the cookies? When asked the first time, I choose "Deny cookies." Later I didn't see where I could allow cookies. I used "reset" and later "default" in the settings at the top right, but the cookie option no longer appeared.
I don't want to discourage you at all as I really appreciate your effort to make "Collapsed Topics Format" available in Moodle 2.3.
With kind regards,
Hartmut