Thanks for the help - i went to the store and got myself another Darkrai code (and a Shiny Charizard code too - bonus!)
Unfortunately the Darkrai code didn't work as i already had it. If anyone is missing a Darkrai for their collection and wants the code feel free to get in touch with me (if you wouldn't mind swapping for my existing one that would be even better).
Just ask someone here with a PAL game that can redeem it for you.