
http://www.guengl.eu/uploads/news-documents/Working_paper_Border_controls_on_cross_border_trade_in_goods.pdf

https://www.opendemocracy.net/en/can-europe-make-it/rest-and-west-thoughts-on-brexit-and-migration-part-one/

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/836116/Explanatory_Note_Accessible.pdf