Settle down with a glass of wine and the radio turned low, and read the 'New Residency Requirements for EU Citizens, including British nationals, who are resident in Spain for more than three months'. It's complicated, written in bureaucratese and it's here. The main concern appears to be protecting the Spanish health service from inappropriate use...
How much money do they think we import to Spain each year?
Why can't we just have a Tarjeta de Residencia?
How far away all this is from the Spirit of Europe is anybody's guess, but Spain has long shown interest in harassing the foreign property owners here, for reasons of their own.