https://blogs.lse.ac.uk/brexit/2019/08/12/boris-johnsons-real-agenda-the-singapore-scenario/
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/397079/Scotland_EnduringSettlement_acc.pdf
https://www.instituteforgovernment.org.uk/sites/default/files/publications/IfG_Brexit_customs_WEB.pdf