https://www.socialeurope.eu/deja-vu-home-office
http://researchbriefings.files.parliament.uk/documents/CBP-7840/CBP-7840.pdf
https://theconversation.com/quien-puede-convertirse-en-ciudadano-espanol-vericuetos-legales-para-obtener-la-nacionalidad-223771
https://www.theguardian.com/politics/2017/may/04/brexit-talks-leadership-vacuum-leaves-45-chance-of-no-deal