As far as I am aware you can't get the Panasonic PHW6 in the UK.
You would have to import one.
The difference in the panel is that the PHW6 is a HD panel and therefore will excel with High definition broadcasts / HD video and so on although, I don't believe the picture quality for lower definition is supposed to be as good as the standard low def panel (PW6).
If its future proofing your after then yes it may be worth the extra.
For the current UK market then probably not worth the trouble.
Others have stated that they believe higher definition can often lead to a softening of the image. Im more of a projector man, but I dont subscribe to resolution increases. My feeling is that there are other factors that are just as important and often ignored. Contrast ratio for instance. As far as im aware, the high def Pannys are not as good as the low.