https://ec.europa.eu/commission/sites/beta-political/files/aviation.pdf
https://institute.global/news/customs-and-exiting-european-union
https://publications.parliament.uk/pa/cm201719/cmselect/cmbeis/379/379.pdf
http://www.russellgroup.ac.uk/media/5521/rg-international-students-june-2017.pdf