
https://www.nao.org.uk/wp-content/uploads/2017/07/The-Customs-Declaration-Service.pdf

http://www.europarl.europa.eu/RegData/etudes/STUD/2017/602028/IPOL_STU(2017)602028_EN.pdf

http://fedtrust.co.uk/our-work-on-europe/brexit-heading-to-a-deal-or-no-deal-while-uk-politics-implodes/