The reality is Deepwater that at some point there will be Companies if they are not already involved, specialising in persuing owners who've walked away from their liabilities in Spain?
I'm not aware myself about any current situations but I do know of a Company who have been successful with chasing Uk owners for unpaid Community Fees for their Spanish Property .
I've recently had contact with a Spanish Lawyer who writes on this Forum (Not Maria) whose been representing clients who wish to hand their property back to the Spanish Banks. The cleanest way he advises, would be to contact the bank, declare your position and discuss a formal procedure for handing back the property. The procedure is called "Dacion en Pago". The owner pays for an independant valuation and that figure is compared with the outstanding balance of the mortgage.
If the value is higher than the loan, the procedure is fairly straight forward. If its less then you would in theory have to pay the bank the difference between the two figures before they would take ownership of the property?
I'm sure most people, particularly ones who are in negative equity will have just handed back the keys and walked away. But theres always the chance that the debt will follow you back to wherever you live at some point and if you have any realisable assets you could end up being sued in the Uk Courts?