http://blogs.lse.ac.uk/brexit/2018/05/15/switzerland-wanted-more-immigration-controls-but-economic-self-interest-will-probably-prevail/
https://www.kcl.ac.uk/policy-institute/assets/uk-attitudes-to-immigration-1018742pub01-115.pdf
https://www.opendemocracy.net/en/beyond-trafficking-and-slavery/exploitation-rule-not-exception/