http://cdn.budgetresponsibility.org.uk/July_2017_Fiscal_risks.pdf
https://www.instituteforgovernment.org.uk/printpdf/10590
http://bruegel.org/wp-content/uploads/2017/03/WP_2017_03-.pdf
https://www.nao.org.uk/wp-content/uploads/2018/10/The-UK-border-preparedness-for-EU-exit.pdf