https://institute.global/news/customs-and-exiting-european-union
https://www.hks.harvard.edu/sites/default/files/centers/mrcbg/programs/senior.fellows/Brexit%20Paper%20IV%20-%20Final%20Paper.pdf
http://ukandeu.ac.uk/brexit-a-french-perspective/
http://data.parliament.uk/writtenevidence/committeeevidence.svc/evidencedocument/treasury-committee/the-uks-economic-relationship-with-the-european-union/oral/72053.html