https://www.nao.org.uk/wp-content/uploads/2017/07/The-Customs-Declaration-Service.pdf
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/637748/Future_customs_arrangements_-_a_future_partnership_paper.pdf
http://fedtrust.co.uk/a-chaotic-brexit-is-still-a-possibility/
https://ukandeu.ac.uk/wp-content/uploads/2020/06/Mind-the-values-gap.pdf