http://fedtrust.co.uk/our-work-on-europe/hard-brexit-international-trade-and-the-wto-scenario/
https://blogs.lse.ac.uk/brexit/2018/10/30/after-brexit-the-uk-should-be-able-to-re-enter-the-eu-if-it-wishes-to-do-so/
https://www.politico.eu/article/eu-uk-relations-rishi-sunak-brexit/
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/640485/Technical_note_on_Functionality_and_Protocol_7.pdf