http://www.nhsconfed.org/-/media/Confederation/Files/public-access/Securing-the-future.pdf?dl=1
https://publications.parliament.uk/pa/ld5801/ldselect/ldeucom/4/4.pdf
https://www.instituteforgovernment.org.uk/sites/default/files/publications/IfG_Brexit_customs_WEB.pdf
https://publications.parliament.uk/pa/cm201719/cmselect/cmcumeds/365/365.pdf