
https://publications.parliament.uk/pa/cm201719/cmselect/cmpubacc/401/401.pdf

https://www.nao.org.uk/wp-content/uploads/2018/10/The-UK-border-preparedness-for-EU-exit.pdf

http://blogs.lse.ac.uk/brexit/2018/09/25/brexit-has-become-unnegotiable-theresa-may-has-a-constitutional-duty-to-admit-that-truth/