https://www.nao.org.uk/wp-content/uploads/2018/10/The-UK-border-preparedness-for-EU-exit.pdf
https://ec.europa.eu/commission/sites/beta-political/files/seminar-20200114-lpf_en.pdf
http://www.conservativehome.com/parliament/2016/04/theresa-mays-speech-on-brexit-full-text.html