
https://theconversation.com/quien-puede-convertirse-en-ciudadano-espanol-vericuetos-legales-para-obtener-la-nacionalidad-223771

https://www.greatbritishpolitics.co.uk/europe/654-dual-nationality-and-the-hurdles-facing-britons-who-want-to-keep-eu-citizenship-after-brexit.html

https://www.kcl.ac.uk/policy-institute/assets/uk-attitudes-to-immigration-1018742pub01-115.pdf