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

https://blogs.lse.ac.uk/brexit/2021/02/04/indyref2-scottish-independence-would-be-2-3-times-more-costly-than-that-of-brexit-and-rejoining-the-eu-wouldnt-make-up-the-difference/

https://publications.parliament.uk/pa/cm201719/cmselect/cmhaff/421/421.pdf