https://publications.parliament.uk/pa/cm201719/cmselect/cmintrade/520/520.pdf
https://www.brookings.edu/articles/what-are-tariffs-and-why-are-they-rising/
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/868378/200227_UK_trade_in_Numbers_full_web_version_final.pdf
http://www.conservativehome.com/parliament/2016/04/theresa-mays-speech-on-brexit-full-text.html