Steve - you may be missing the fine line between "legal" and "needed".
The 10 hours allowed "legally" in the US will probably be re-flown in the UK training system - it will not be a saving, as such, AND if you do the ten hours early in your course, you will have to be re-trained when you get back to the UK system - to get you out of doing what you have just been taught.
The FAA system and syllabus is different - and it will not get you through a JAA flight test flown in the UK (or, at least, it shouldn't).