Posted: Sun Aug 8, 2021 1:17pm
Mel, I cannot see that anyone on this Forum could tell you for sure what will happen when you arrive back in Spain. It sounds to me like you are legal because you will have the paper work that states your application is in process (I presume) and you have not overstayed your 90 days.
I suppose there are some possible wrinkles that you could face depending on a return flight date and bumping into a border guard in a bad mood.
This is difficult in Spain because no matter who you talk to, even lawyers, you will get a number of opinions because I believe that no one knows for sure what the official will do when you come through Customs returning from the UK. But you sound legal if your paperwork is all in order and you have not exceeded 90 days. Just be sure to have everything in order to demonstrate your legal.
Good luck!