Upvote:0
Your citizenship is not clear.
a common format residence permit issued by an European Economic Area (EEA) country or Switzerland
Since you have a resident card for Spain, you don't need to take a transit visa.
Check by yourself here - https://www.gov.uk/check-uk-visa
Upvote:1
You can see the current rules for transiting the UK on the Gov website found here:
https://www.gov.uk/government/publications/uk-visa-requirements-list-for-carriers
It is updated regularly so it is best to use the link rather than downloading the PDF. This is a guide to help airlines understand the rules for transiting the UK.
Or you can also see here by answering a few questions if a visa is needed or the rules for transit without a visa depending on your specific circumstances: