Any time you spent in Spain or other Schengen countries before 1 January 2021 does not count towards your 90-day visa-free limit.
At Spanish border control, you may need to use separate lanes from EU, EEA and Swiss citizens when queueing. Your passport may be stamped on entry and exit. You may also need to:
show a return or onward ticket
show you have enough money for your stay
show proof of accommodation for your stay, for example, a hotel booking confirmation, proof of address if visiting your own property (e.g. second home), or an invitation from your host or proof of their address if staying with a third party, friends or family. The Spanish Government has clarified that the “carta de invitation” is one of the options available to prove that you have accommodation if staying with friends or family. More information is available from the Spanish Ministry of Interior.
There are separate requirements for those who are resident in Spain. If you are resident in Spain, you should carry proof of residence as well as your valid passport when you travel. For further information see Requirements for UK nationals resident in Spain.
That’s on the U.K. Gov site.
