
https://www.gov.uk/government/speeches/commonwealth-has-key-role-to-play-in-the-bright-future-for-britain-article-by-boris-johnson

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

http://www.europarl.europa.eu/RegData/etudes/IDAN/2017/599352/EPRS_IDA%282017%29599352_EN.pdf