https://publications.parliament.uk/pa/cm201719/cmselect/cmworpen/848/848.pdf
https://www.instituteforgovernment.org.uk/sites/default/files/publications/negotiating-brexit-preparing-talks-uk-future-relationship-eu-FINAL_1.pdf
http://blogs.lse.ac.uk/brexit/2018/09/25/brexit-has-become-unnegotiable-theresa-may-has-a-constitutional-duty-to-admit-that-truth/
https://www.iod.com/Portals/0/PDFs/Campaigns%20and%20Reports/Europe%20and%20trade/Business-of-Brexit.pdf?ver=2017-05-22-090428-150