I have no doubt that a European Army will happen. But the UK will not join.
22 EU countries are already in a joint army, it is called NATO.
The Reason the EU constantly fails to secure its own external borders, is because individual coumtries are tasked with the job, and they are not up with it. A co-ordinated pan Europe effort could not do any worse.
The Former Field Marshall says we should stick with the Americans. There is no reason we cannot fight alongside the EU and the Americans. The Americans have dragged us into Afghanistan, Iraq and Syria. There might be instances where Americas interest is different from ours. The US invaded Grenada, sovereign British territory, not too long ago. Likewise, our NATO partner Turkey might have different priorities than Europe, and Europe needs to have an alternative to that.
Isn't there a term for someone who switches sides mid-battle?