Making a Spanish Will is not compulsory but highly advised. Please note that a British will is totally valid in Spain and even if someone dies in-testate, the Spanish assets will be dealt with according to In-testate documents granted by the deceased’s national authorities.
However, having said this, drawing up a will in Spain to cover only the Spanish assets, makes the whole procedure a lot easier, less expensive and above all, less stressful for the beneficiaries. It is unnecessary to present any kind of documents which are unknown to the Spanish Authorities (although they may be totally legal in the country of expedition) and it also saves expenses of official translations into Spanish and International Apostilles.
All wills made in Spain are registered in one central Registry, which makes it easy to apply for a certificate in the event of having to find out what someone’s Last Will and Testament entails. This tells the person where the will was actually signed and can be obtained within a few days. The system is so simple and straightforward here, that it would be a pity not to take advantage of it!
The best reason to make a Spanish will is that it will make it much easier to administer your Spanish estate upon your death. In fact a well drafted English will can have the same results, but if you have the option it is always better to deal with your Spanish assets in a Spanish will.