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Microsoft are still working on the UK version, it is supposedly close to being ready but all they have said is it will be "late this year"
i also did the same thing on my test
phone lumia 520 and it does work
once you change the region and make
the usa as default all you need do after
that is restart your phone and cortana will
be there settings then swipe to applictions
and she will be on that list just put a few deatils
and it's up and running
thanks for the replies, got it to work yesterday as sugested by changing both settings. Only drawback is you have to leave the settings in usa option to carry on using it.