bellow is from gov web site this is still in force util 30th may but could change always worth checking daily if you are planing on traveling . you also need a PCR negative fit to fly taken min 72 hours before flight and you have to complete health entry form online to obtain QR code.
Also note when you read bellow that even with the correct papers the final derision is with the border control officer . No more electric barriers you have to present your passport and papers to the officer and have passport stamped and if he or she is having a bad day you could be refused entry ( you can thank Brexit for that one you also have to have your passport stamped when leaving)
I have made the journey twice in the last 2 months for work and even with the correct papers it is not a fun journey especially as almost no direct flights so had to go through Madrid meaning double checks on everything. Lets pray we can get back to some normality soon.
Bellow is taken from the web site
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 (Resguardo 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, 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 may be presented. However, due to current travel restrictions, be aware that you may be questioned on arrival by Spanish border authorities to ensure you meet the legal entry requirements. Spanish border authorities will only grant entry if they are satisfied that you are returning to Spain to your habitual place of residence or can demonstrate an essential reason to enter (see ‘Permitted reasons to enter Spain’), and reserve the right to deny passage.
The above list of documentation has also been communicated to airlines and other operators.
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