https://www.nao.org.uk/wp-content/uploads/2018/10/The-UK-border-preparedness-for-EU-exit.pdf
https://committees.parliament.uk/oralevidence/2766/pdf/
https://www.conservativehome.com/parliament/2018/07/our-brexit-plan-takes-back-control-of-money-laws-and-borders-and-heres-how-may-and-raabs-letter-to-conservative-mps.html
https://voxeu.org/system/files/epublication/Economics%20of%20Brexit.pdf