https://ec.europa.eu/commission/sites/beta-political/files/customs_controls_0.pdf
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/397079/Scotland_EnduringSettlement_acc.pdf
https://www.open-britain.co.uk/new_research_trade_deals_with_five_key_countries_could_take_26_years_to_negotiate