https://www.nao.org.uk/wp-content/uploads/2017/07/The-Customs-Declaration-Service.pdf
https://www.socialeurope.eu/wp-content/uploads/2019/01/03_Brexit_Kroeger.pdf
http://www.cesifo-group.de/portal/page/portal/DocBase_Service/studien/Studie-2017-Felbermayr-etal-Brexit-79843.pdf
https://www.regjeringen.no/globalassets/upload/kilde/fkd/red/2004/0009/ddd/pdfv/228920-nilf_rapport_2004_9_s.pdf