https://www.instituteforgovernment.org.uk/explainers/eu-withdrawal-bill-amendments-and-debates
http://fedtrust.co.uk/views-from-the-federal-trust/free-movement-and-migration/
https://www.gov.uk/guidance/status-of-eu-nationals-in-the-uk-what-you-need-to-know
http://www.cer.org.uk/sites/default/files/insight_JS_9.5.17.pdf