Spanish citizen working for UK charity remotely from Spain

Hi! I am a Spanish citizen (living in the UK for +9 years) and will soon be a UK citizen as well. I am currently working for a UK-based INGO and want to request moving to Spain while still working remotely for them. What would be the implications (admin/tax) for both me and my employer? What options would I have that would mean no extra cost for my employer? Information online seems to be conflicting. The INGO does not have a tax residency in Spain (neither they want to). Thanks!

Hi iria,
Please refer to the following Guidance -
Employees working abroad and Tax if you leave the UK to live abroad.
Thank you.