https://ec.europa.eu/commission/sites/beta-political/files/joint_report.pdf
https://ukandeu.ac.uk/wp-content/uploads/2020/05/UKICE-Post-Brexit-Gov-NI-Report.pdf
https://committees.parliament.uk/oralevidence/2766/pdf/
http://www.guengl.eu/uploads/news-documents/Working_paper_Border_controls_on_cross_border_trade_in_goods.pdf