The flags in question are not being flown as flags. That would be fine. They are being used as decoration because of Euro 2016 football tournament. Because they are decorations, they all under the rules for displays at polling places.
If EU flags were being displayed as decorations at a polling place, they’d be removed as well - and some people would have done it.
Understand I am a very strong supporter of the St George’s flag as a symbol of England and think it should be flown more widely than it is, and object to those who want to paint it as somehow racist.
But it very important that the rules concerning neutrality are followed in elections, because if they are not, the left will take much greater advantage of that than anybody else.