https://institute.global/news/customs-and-exiting-european-union
http://UK Brexit And The Exterminating Angel
http://www.epc.eu/documents/uploads/pub_7788_whatnowoptionsforbrexit.pdf?cmpid=BBBXT061617_BIZ&utm_medium=email&utm_source=newsletter&utm_term=170616&utm_campaign=brexit
https://publications.parliament.uk/pa/ld201719/ldselect/ldeucom/9/9.pdf