The UK Government has published new information regarding the documents that UK citizens who reside in Spain can show if they wish to return to Spain from the UK while the travel restrictions are in place.
In order to make sure that the Spanish authorities confirm these new options, I sent an email to the Spanish Consulate in London and they sent me the following link:
https://www.gov.uk/foreign-travel-advice/spain/entry-requirements
This link informs as follows:
Additional requirements for UK nationals resident in Spain
The Spanish government has formally confirmed to the UK government that UK nationals who were legally residing in Spain before 1 January 2021, and as such are beneficiaries of the Withdrawal Agreement, can use any of the following documents to prove their residence status when entering Spain:
Residence card issued under Article 18.4 of the Withdrawal Agreement (the TIE – Tarjeta de Identidad de Extranjero)
Temporary or permanent EU residence certificate (Certificado de Registro de Ciudadanos de la Unión)
Receipt of application for the TIE (Resgaurdo de presentación de la solicitud de la tarjeta de residencia)
Confirmation of the positive outcome of your residence application (Resolución favorable por la que se concede la tarjeta de residencia)
In the absence of any of the above documents, other documents that credibly evidence your legal residence in Spain before 1 January 2021, such as a padrón certificate (issued by your town hall), a work contract, a rental contract, or proof of property purchase
In the case of students, documentation that demonstrates enrolment in an on-site or in-person course and proof of accommodation
You must also show a valid passport when you travel and comply with the other documentation requirements, such as a negative COVID test within 72 hours of arrival, as set out in this travel advice.
The above list of documentation has also been communicated to airlines and other operators.
As you can see, this opens the doors for many UK citizens who have their place of residence in Spain to finally return home.