http://fedtrust.co.uk/the-2017-general-election-a-mandate-for-brexit/
https://ec.europa.eu/commission/publications/position-paper-essential-principles-financial-settlement_en
https://www.gov.uk/government/news/programme-for-fourth-round-of-uk-eu-article-50-negotiations
https://www.ifs.org.uk/publications/10302