Amendment for those who may have thought I was referring to Spaniards who acquired a second nationality:-
Take care, if a person has acquires a Spanish passport nationality (so not a Spaniard) they are forbidden by Spain to also have a UK one another (dual nationality) . Only citizens from former Spanish colonies, Columbia, Philippines etc are permitted to have dual nationality
https://en.wikipedia.org/wiki/Spanish_nationality_law
On the other hand, foreign nationals that acquire Spanish nationality lose their previous nationality, unless they were natural born citizens of an Iberoamerican country, Andorra, the Philippines, Equatorial Guinea or Portugal.
http://www.dualcitizenship.com/free-consultation/spain.html
For those seeking to acquire Spanish citizenship as their second citizenship, whether or not the person can retain dual citizenship depends on the county in which they hold their original citizenship. For example, if a U.S. citizen acquires Spanish citizenship, Spain requires the person to renounce U.S. citizenship, but this is usually insufficient for the American to lose U.S. citizenship. In this scenario, Spain will view the person as solely a Spanish citizen, whereas the U.S. will still treat the individual as an American citizen. Practically, the individual will hold U.S. and Spanish dual citizenship.
This message was last edited by johnzx on 04/01/2016.