Free movement of people to the impoverishment and even endangerment of the citizens in a given nation is a recipe for exactly what has happened, and not just in Great Britain. There needs to be plausible reason to increase immigration, and there needs to be penalty for prospective immigration from groups that prove to be hostile. Otherwise, the citizens will continue to oppose such policies.
We have a Constitution consisting of 4 pages of principles of limited government. The EU has a Constitution that is HUNDREDS of pages long and amounts to a suicide pact.