OK I tried resubmitting it with the same result, so then I tried changing the sitemap so that it now has the following priorities:
This gives the top domain, the .co.uk, and the index.html page the same priority, because they are the same thing, and then the other two pages priorities of 0.8.
However, Google downloaded the file 15 hours ago and still says "All the URLs in your Sitemap are set to the same priority" which seems to be a bit nuts: after all 1.00 is not the same as 0.80!
I am going to try changing them ALL to different values now to see if I can get to the bottom of this, but I would really like to know what is going on?!?!?
Regards - Brogden