Also a recent law forces you to declare all assets held outside Spain in various categories: Capital (such as a house), bank accounts and so on. If any of these exceeds 50000 euro, you must declare it to the Spanish taxman. And of course just about any flat or house in the UK is worth more than that. I dont think they TAX you on these resources….yet.
For this reason, I, for one, think it may be better – certainly simpler -to be officially non-resident in Spain and not to own property there.