well... really back in the mists of time, it was the Great Britain Pound because the pound sterling antedates the existence of the United Kingdom by several centuries. Saying UKP is acceptable (although people may judge you for it) in the sense that I had no difficulty figuring out what you meant but the biggest impediment today is computers since no computer is going to let you buy or sell or bank UKP. The whole identity crisis that these people have is tiresome for everyone else, though. Layer into the equation "the English" and "England." It took me 2 years of living in England with someone who denied his English-ness to fully (not) understand. Oh, and when he spoke to his family in "English," my head nearly spun off.