Thanks - first I didn't realise there was a 'Display Newest First' option, but I have found that and ticked it and still the products appear in alphabetical order (which in itself is strange). so I changed the code as you suggested above and it has certainly taken the products out of alphabetical order, and they do start to appear in order of latest ID, but two problems:
First the latest ID is at the bottom of the page not the top and second, then if you follow the product IDs upwards when you get about half way up a page they appear random - not in product ID order.
Looking at your code, am I right in assuming (not being a coder myself!) that they should appear in date_added order? If so, that could be a problem because when I look at the database, since the upgrade all the dates are now zero.
So is there a way to make the products appear in latest ID order?
Many thanks