http://www.esf.be/new/wp-content/uploads/2018/07/ESF-Press-Release-on-Importance-of-Services-Trade-in-EU-UK-Future-Relastionship.pdf
https://www.bloomberg.com/news/articles/2019-09-11/world-s-oldest-customs-union-and-u-k-reach-a-post-brexit-deal
https://publications.parliament.uk/pa/ld201719/ldselect/ldeucom/387/387.pdf