So when someone says that “x will lose out”, that may also mean that y will win-out. This is true about all economic policies: from Stalin's to “austerity” and Brexit.
So, in the end, there has to be more to this debate that economics.
The European Union is attempting to fill the UK with masses of immigrants - many of whom aren't happy with our culture, laws and traditions.
The EU's also taking away our rights with one hand and creating laws that suffocate us with the other.
In the end, I see the “democratic deficit” to be far more important than economics because economic reality always rides on the back of political changes – contrary to what Marx argued.