Here's the skinny Marc: if a set has a built-in digital tuner it is an HDTV set. If the set has no built-in digital tuner but can display HDTV signals from an external tuner, then it is HD-Ready. I'm not sure why Dell is labeling this set as "HD-Ready" but my guess is that there are different labeling standards in the UK than in the United States.
The good news is: regardless of what the label says, you've got yourself a solid HDTV set. Cheers mate!