Jeff, and Alan,

Initial play around with has allowed me to find that:

Firstly, the Kindle doesn't recognise the HTML extension and HTML files
copied onto the Kindle simply don't appear as being available for viewing.
If you change the extension to txt, the file appears and can be seen as an
HTML files but includes some spuriois HTML code.

The Orgmode to XHTML to SIGIL to ePub to Calibre to MOBI (for the Kindle)
works extremely well, and for proper books looks good.

But for quick updates Calibre wil read the HTML files directly and will
convert to MOBI reasonably well, if its simple text and simple tables.

This is stll better than Orgmode to PDF to Calibre to MOBI,  as this route
breaks even simple tables.

Thanks for the help.

Graham