Hello XL,
you posted this in the professional section, so I assume you will go on to CPL. Why would you invest such a large sum of money into something that you will use probably no more than a year? A JAA PPL will be gone once you upgrade. Any other PPL will be yours for life, and that is all that is needed to commence ATPL studies.
The exchange rate is one factor for more expensive PPLs than in the US, but most places in Europe are cheaper (for pretty much anything). You generally pay in Euros what you pay in Pounds in the UK (plus the extra travel, accommodation, etc.).
If you then still really want a UK issued PPL, it's a straight swap. Please don't believe that standards anywhere outside the UK are lower, and if you have to spend a little extra to get used to UK airspace, you still save a bunch and build hours, not to speak of experience gained abroad...