Hello, yes, there are loads of HD movies available from the UK store via Apple TV.
All you need to do is go to the 'HD' section of the movies menu from the Apple TV.
Also, if you select any particular movie, the iTunes store will tell you if a HD version is available.
I must have seen 3 or 4 movies this was this month alone.
If you do not have an Apple TV in then HD will no show up as an option when viewing iTunes store on your computer.
The itunes store needs to now that you have Apple TV before it will offer you HD movies. Not sure if this works because you have already registered your Apple TV against your itunes account or if the iTunes store somehow detects your Apple TV.