The HC3 from the USA will record in NTSC (well sort of in HD ) and in the UK our TV is PAL.
Although HD video is stricktly not NTSC or PAL it does have a refresh rate of 60htz (USA) or 50htz (UK) that will cause problems if recording to VHS and possibly even a settop DVD recorder. These problems should be less if the DVD is created on a PC/Mac.
Other things to think about are:
Should it break down you may have trouble getting Sony UK to do a repair on a unit they made no money out of when it was purchased.
If customs catch you on your way back into the UK the money saved getting it from the USA may be lost.
I suggest you do a search of the forum on further advice on buying from the USA as it has been covered many times in the past and most if not all of it should still apply.