An annual trip to Carlos Albacar in Tortosa to enter the annual tax return and direct debits for local and national taxes, electric water etc.  A private health insurance plan.  Vehicle registered to Spanish plates, road tax and insurance.  Stay legal and relax.
It also means no access to the N.H.S. in the U.K. as that is a residence based service.  I may review the situation after my retirement, time will tell. :)