I've received the Limited Edition game from Amazon.co.uk today, but I'm not sure how to activate the PRE ORDER content?
It certainly doesn't seem to be already in the game?
It should be inside the case, behind the manual.
The pre-order content is a code which you need to input online, your game should have come with this. Just open Xbox Marketplace, PSN Store, or Steam, find the Redeem Code feature and put your code in.