https://theconversation.com/why-the-eus-singapore-ruling-does-not-lead-to-a-smoother-brexit-road-for-britain-78116
https://publications.parliament.uk/pa/cm201719/cmselect/cmbeis/379/379.pdf
https://www.cer.eu/sites/default/files/insight_SL_5.11.19_2.pdf