Exactly^
If in the future, England decided to declare war against a country linked or related to the EU, the states would decide whether to settle this situation. If we were to be left an independant country, we'd have both a war commencing and political chit chat whether to prevent us from attacking.
Its up to the council to decide if they should engage or not and seeing that England does alot to fund the EU, I very much doubt all th EU states would avenge us due to various reasons.
Ofcourse the EU wasn't formed to make a strong military force, we know what it was formed for. Obviously we would still have allies whether or not we did have a war, like I said, our trade is highly demanded for, the UK is used to house millions of foreign families, turning agaisnt us would make the matter worse.