https://ec.europa.eu/commission/sites/beta-political/files/guiding-principles-dialogue-ei-ni_en.pdf
https://publications.parliament.uk/pa/cm201719/cmselect/cmpubacc/401/401.pdf
https://www.instituteforgovernment.org.uk/sites/default/files/publications/5704%20IFG%20-%20Frictionless%20Trade%20Web.pdf
http://blogactiv.eu/blog/2012/05/15/stumbling-towards-the-brexit/