https://www.theguardian.com/politics/2017/sep/04/uk-trade-deals-after-brexit-theresa-may-eu
https://blogs.lse.ac.uk/brexit/2021/01/11/article-16-of-the-ireland-northern-ireland-protocol-offers-no-quick-fix/
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/637748/Future_customs_arrangements_-_a_future_partnership_paper.pdf
https://www.instituteforgovernment.org.uk/sites/default/files/publications/IfG_Brexit_customs_WEB.pdf