This is from the Royal Mail site,
https://business.help.royalmail.com/app/answers/detail/a_id/520/~/help-tracking-items-posted-to-another-country-from-the-uk
"What happens after my item's left the UK?
For certain European destinations, we use a Royal Mail Group Limited company called GLS. You can use GLS to track International Tracked & Signed items sent to the following countries:
Austria (for International Tracked and International Tracked & Signed), Bulgaria, Czech Republic, Germany, Greece, Hungary, Luxembourg, Poland, Portugal, Romania, Slovakia and Slovenia
For other destinations, once your item has left the UK we hand it over to the relevant country's postal authority. They deliver it on our behalf and let us know some of the details of your item's journey.
For some destinations you may be able to see more detailed tracking on that postal authority's website**. Below are links to the most popular destinations:
Australia
France
Germany
Republic of Ireland
Spain
United States of America
Alternatively visit the Universal Postal Union to see if the country you've posted to has a tracking website where you can obtain more information.
**Please note extra tracking information is not guaranteed or a part of the service you've purchased. It's offered over and above the service requirements and we cannot guarantee its accuracy."
GLS would not have been involved since the address is in Spain.