https://ec.europa.eu/info/sites/info/files/com-2018-890-final.pdf
http://www.rug.nl/research/portal/files/41711829/cesifo1_wp6448.pdf
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/831199/20190802_Latest_Yellowhammer_Planning_assumptions_CDL.pdf
https://www.parliament.uk/documents/commons-committees/culture-media-and-sport/Background%20paper%20-%202016%20Referendum%20Expenses%20Opinion%20-%20Matrix%20Chambers.pdf