When faced with the possibility of cooperating for mutual gain, states that feel insecure must ask how the gain will be divided..
A state worries about a division of possible gains that may favor others more than itself. That is the first way in which the structure of international politics limits the cooperation of states. A state also worries lest it become dependent on others through cooperative endeavors and exchanges of goods and services... The world's well-being would be increased if an ever more elaborate divisions of labor were developed, but states would thereby place themselves in situations of ever closer interdependence...
In an unorganized realm each unit's incentive is to put itself in a position to be able to take care of itself since no one can be counted on to do so. The international imperative is "take care of yourself"! Some leaders of nations may understand that the well-being of all of them would increase in their participation in a fuller division of labor. But to act on the idea would be to act on a domestic imperative, an imperative that does not run internationally...Waltz's argument may not apply perfectly to the EU, since he claims that the fundamental impediment to cooperation is the threat of conflict. The era of European wars is long over, but there may nonetheless be something to Waltz's argument. In the midst of economic crisis, tensions between European countries have hardened, and the crisis has caused bickering among EU member nations.
On another note, a recent FT/Harris poll of the British public found that only one in three Brits wants to remain in the EU.