If you’re moving anywhere near LLanes (Asturias), and looking for a UK branded bank, then there’s a Barclays in town.
In addition, Abbey (now part of Grupo Santander), will arrange a Spanish Morgage etc. through Banco Santander. For the UK, this is all run from a London office, I don’t know if they have something similar for Ireland.
In general, upfront charges are higher (a lot) on mortgages taken out with Spanish Banks, but you benefit from a lower interest rate. Also watch out for hefty additional charges / restrictions, such as capital payments, early redemption etc.