Ok, more reveals slightly more success.
When making Ene's change, it doesn't seem to work unless you place his line of code ahead of this code:
Code:
if (!empty($cat))
include "./products.php";
It would normally come after this code and, left in that position, the change doesn't seem to have any effect.
Then, if you also make Verfurt's change the featured product box does appear on the category page. Further, moving the code up the file moves the featured product box position on the web page. That's all good and a step forward.
The problem is that by making the change that Ene suggests and moving it as I've indicated, for any categories that have more than one page the navigation bar is no longer displayed. So, if we can just solve that issue then all will be hunky dory.