https://publications.parliament.uk/pa/ld201719/ldselect/ldeucom/129/129.pdf
https://www.instituteforgovernment.org.uk/printpdf/10590
https://institute.global/news/the-inbetweener-brexit
https://www.bloomberg.com/news/articles/2019-09-11/world-s-oldest-customs-union-and-u-k-reach-a-post-brexit-deal