The answer is yes, unless your Will explicitly excludes your Spanish property or states that it only applies to property which you own in the UK, for instance. Otherwise, your Will takes effect over your assets on a world-wide basis.
The question is whether this is the most sensible approach and there is no easy answer to this. There are advantages in having one world-wide Will, to include your Spanish assets, since then there is no danger of having conflicting Wills or of one of the Wills accidentally cancelling the other one. It should also make the Will easier to understand and the making of the Will should be a cheaper exercise overall.
On the other hand, overseas countries in Europe do not like trust concepts and the Spanish legal system will find it harder to deal with an English or Welsh Will. With that in mind, we would generally suggest having a separate Will in Spain in respect of your Spanish assets only and ensuring not only that you have a proper translation of the Spanish Will but that whoever is responsible for your UK Will has a copy of that translation, so that they can check that there are no provisions in it which would clash with the UK position.
This is a complicated area of law and practice, which has not been helped by recent changes in European legislation, which are intended to decide which legal system will apply on your death (the Spanish one or UK). It is therefore strongly recommended that you take proper legal advice – to speak to Adam Bruce who is experienced in this area of law, please either telephone 01267 239196 or e-mail him at firstname.lastname@example.org