
https://ec.europa.eu/commission/publications/position-paper-transmitted-eu27-ongoing-police-and-judicial-cooperation-criminal-matters_en

http://www.cesifo-group.de/ifoHome/publications/working-papers/CESifoWP/CESifoWPdetails?wp_num=6448&CESifoWP.search=+

https://www.instituteforgovernment.org.uk/sites/default/files/publications/IfG_Brexit_customs_WEB.pdf