If you're counting down the hours until midnight for Pokemon X and Y to release in the UK, put away your pocketwatch and make haste to your horseless carriage. Major retailer GAME has broken the worldwide street date for the title and is selling it nationwide as of now.
GAME told Polygon that it disregarded Nintendo's very serious (it is really not kidding around, here) launch window because "a competitor broke street date--so other retailers can now sell this title." It refused to name the competitor and directed further questions to Nintendo.
We doubt Nintendo is very happy about this turn of events, given that this is the first-ever simultaneous worldwide release for the 17-year-old RPG series. That doesn't mean you shouldn't take advantage of it, though--even if you pre-ordered somewhere else, there's a decent chance your retailer of choice is starting early in response.