For information on correctly registering your residency as a British national living in Spain see the UK govt’s website link https://www.gov.uk/guidance/living-in-spain (external link),

The previous content on this page you are looking at now has been discontinued as the process for asking for residency as a British resident changed from July 2020. You can see more information from us here. https://www.supportinspain.info/knowledge-base/how-do-i-1-get-an-nie-2-register-as-officially-resident-in-spain-or-3-get-on-the-padrontown-hall-census/ 

or  https://www.supportinspain.info/brexit-update/