https://www.hamiltonproject.org/assets/files/UnionsEA_Web_8.19.pdf
http://futurion.se/wp-content/uploads/2018/03/Futurion_Rapport_2018-1_webb.pdf
http://sprc.info/wp-content/uploads/2012/07/Polish-Migrants-in-London-extending-the-stay.pdf
https://www.ceps.eu/system/files/CEPS%20-%20LINKEDIN%20study%20FINAL.pdf