https://www.instituteforgovernment.org.uk/sites/default/files/publications/IfG_Brexit_customs_WEB.pdf
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/704057/Policy_Note_-_Exceptions_and_Licences.pdf
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/638135/6.3703_DEXEU_Northern_Ireland_and_Ireland_INTERACTIVE.pdf