http://ec.europa.eu/eurostat/statistics-explained/index.php/Acquisition_of_citizenship_statistics
http://www.migrationobservatory.ox.ac.uk/resources/commentaries/brexodus-migration-and-uncertainty-after-the-eu-referendum/
https://www.aicgs.org/publication/refugees-terrorism-and-a-failing-security-architecture/
https://www.gov.uk/guidance/status-of-eu-nationals-in-the-uk-what-you-need-to-know