https://ec.europa.eu/commission/sites/beta-political/files/customs_controls_0.pdf
https://publications.parliament.uk/pa/cm201719/cmselect/cmbeis/380/380.pdf
https://www.wto.org/english/res_e/booksp_e/wtr23_e/wtr23_e.pdf
https://www.gov.uk/government/speeches/eu-speech-at-bloomberg