https://publications.parliament.uk/pa/cm201719/cmselect/cmintrade/520/520.pdf
https://www.nao.org.uk/wp-content/uploads/2017/07/The-Customs-Declaration-Service.pdf
http://ecipe.org/publications/the-uks-first-international-trade-negotiation/?chapter=all
https://ec.europa.eu/commission/sites/beta-political/files/joint_table_citizens_rights_-_third_round.pdf