https://www.nao.org.uk/wp-content/uploads/2017/07/The-Customs-Declaration-Service.pdf
https://www.opendemocracy.net/en/opendemocracyuk/customs-union-leaves-everything-play-trade-justice/?utm_source=Daily+Newsletter&utm_campaign=f531c721c4-DAILY_NEWSLETTER_MAILCHIMP&utm_medium=email&utm_term=0_717bc5d86d-f531c721c4-407405485
https://ukandeu.ac.uk/wp-content/uploads/2021/02/UK-regulation-after-Brexit.pdf?mc_cid=1d4cf56e72&mc_eid=815b1928ec
http://www.coggs.polis.cam.ac.uk/news/forum-on-geopolitics-triple-bill-on-brexit