Hi Paul,
First, thanks for our rapid response -
The document I am working on is a template where the page numbering is defined and updated from the ribbon (I have added a tab and relevant button).
The original solution worked well because the numbering was reasonably simple to construct. The front matter was roman letters (e.g. Page i of vii) and the body and appendices were arabic numbers (e.g. Page 4 of 45) where page 45 was at the end of the document and included the appendices. The page number of the split was easy to determine because the first Heading 1 had a fixed title "Executive Summary" and so was easy to select.
However, the "powers that be" have now decided that the appendices should not be numbered and the numbering should end on the last page before the appendices start. This means I need to determine the page number of the first appendix and use that (minus 1) to determine the total number of pages in the main body. (Hope that makes sense and is not too obtuse.)

Hold everything I might have a solution:
If I place the cursor at the start of the doc and then use Find to locate a heading 6 it must go to the first instance (of heading 6 in the doc). I will let you know if that works...