https://institute.global/news/customs-and-exiting-european-union
https://www.instituteforgovernment.org.uk/sites/default/files/publications/negotiating-brexit-preparing-talks-uk-future-relationship-eu-FINAL_1.pdf
https://www.nao.org.uk/wp-content/uploads/2018/10/The-UK-border-preparedness-for-EU-exit.pdf
https://ec.europa.eu/commission/sites/beta-political/files/use-data-protection-information_en.pdf