
http://www.guengl.eu/uploads/news-documents/Working_paper_Border_controls_on_cross_border_trade_in_goods.pdf

https://www.publications.parliament.uk/pa/cm201617/cmselect/cmbeis/909/909.pdf

http://www.russellgroup.ac.uk/media/5521/rg-international-students-june-2017.pdf