Thanks again, Geert!
The first issue turned out to be that it was not picking up #DIAGRAMID#, which was down to the template not being in the right place (as I didn't think, from the Help, that templates could apply to diagrams)... Once I hard coded the value to experiment with I was able to start to generate some information...
I then ended up with duplicates, this was due to leaving some of the sections on that we effectively being generated by my fragment... and because I'd put it in the Element section it was running the fragment for each element - which caused a lot of duplication!
The only issue is now that the notes, which are in RTF in the model come out as HTML in the report. This is not a showstopper, as they were only really experimentally RTF, so I can live with that not working...
Thanks for the nudges in the right direction, I hope that I can take it from here...