Federated European Army is Britain's nightmare, in terms of geopolitics, from the historic perspective. 

One of the ultimate long term goals for the Great Britain is to remain as the counter balance of the european powers, and the ultimate arbitrator of the european conflict. To do that, it is its national interests to ensure the "de-integration" of the european powers, while maintain the peace on this vast neighboring continent. The consolidation of the european powers, especially Germany and France, will dethrone the UK as the second major power after US in the region, and the world. Remaining inside if EU will ensure that european is collaborating, rather than integrating. Now the country is leaving this organization, paving the way for the true integration, led by France and Germany, its two historical rivals. British is feeling the cold.

The only viable solution is to leverage British role in the NATO to discourage, even bar the creation of any form of the Euro Army. Will it achieve the goal? The time will tell.

Google translation:

联合欧洲军队是英国的噩梦，在地缘政治方面，从历史的角度。 一个为英国最终长远目标是继续作为欧洲列强的反平衡，以及欧洲冲突的最终仲裁员。要做到这一点，这是它的国家利益，以确保欧洲列强的“去一体化”，而维持这个庞大邻国的大陆和平。的欧洲列强，尤其是德国和法国，合并将废黜英国成为美国之后的第二大力量在该地区，乃至全世界。剩余里面，如果欧盟将确保欧洲是合作，而不是整合。现在国家正在离开这个组织，铺平了真正的整合，法国和德国，它的两个竞争对手的历史一马当先。英国是感觉寒冷。 唯一可行的解决方案是利用北约的英国角色劝阻，甚至禁止任何形式的欧洲军队的创建。它会实现这个目标？时间会证明一切。