https://www.gov.uk/guidance/status-of-eu-nationals-in-the-uk-what-you-need-to-know
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/695321/An_inspection_of_exit_checks.pdf
http://www.cesifo-group.de/portal/page/portal/DocBase_Service/studien/Studie-2017-Felbermayr-etal-Brexit-79843.pdf
https://blogs.lse.ac.uk/brexit/2020/10/22/the-cost-of-brexit-is-likely-to-be-more-than-double-that-of-covid-it-must-be-delayed/