Government sources confirmed on Sunday evening that despite having left the bloc earlier this year, the United Kingdom is still considered an EU member state given that it is in a transition period and enjoys full membership rights. This means that UK travelers will also be able to enter Spain from June 21.
If we were outside the EU I would suspect they would treat us as a favoured nation due to the massive tourist trade from the UK.
The fly in the paella is that the UK still has an all but essentially travel warning still in force and a quarantine for returning visitors.
This will probably do Spain a favour by keeping new cases out of their country for a few more weeks.