Originally Posted by EverHopeful
you will not have an issue, but in case of disasters, legal issues and the like Spain will not recognise your British nationality and will not give the British consulate access whilst you are located in Spain. As regards health care, I have no idea, but given you have not lived in Spain nor paid into the system you may not have automatic access.
I recall that we have/had a forum member from Canada (AllHeart) who obtained Spanish nationality by reason of the fact that her father was Spanish, then moved here. She started to receive health treatment here in Spain (including cancer treatment) immediately despite never having paid Spanish social security.