Directly from the National Lottery website:
"Can I play while overseas?
No, to play UK National Lottery games online, you must be a resident of the UK or Isle of Man at all times. You must also be physically located in the UK or Isle of Man when buying a ticket or when setting up or amending a Direct Debit Account, including changing your numbers and payment details.
If you do not meet these requirements, any ticket purchases you make will be declared invalid and no prizes paid, and we will have the right to reclaim any prizes already paid under these circumstances".
http://www.national-l...s.ftl#int_GetStarted2
Chris