The Foreign Office has updated Spain's entry requirements amid a change to their travel rules.
Previously, every person entering the country, even with a certificate, had to fill out the form in order to receive a QR code to present at the airport upon arrival. But now the rules have changed and travellers with an EU Digital covid Certificate or equivalent from a non-EU country will only have to show their certificate when they arrive, without having to complete the health form as well.
Spain has a Travel Health Control form which you must complete no more than 48 hours before travelling to Spain unless you have a digital covid-19 certificate.