Driving in Spain
If you have a car with British or German registration, as a tourist, you will be able to operate with the car for six months of each calendar year. With Spain’s entry into the EU, the international insurance certificate is no longer necessary.
Your driving licence from your home country is acceptable for six months in Spain however authorities recommend that you have either an international driving licence or an official translation of your licence, which you can be obtained from the Spanish Consulate in your home country.
The six month period is based on the stay of the person himself in the country. The thing is how do they know whether or not you are driving the car? There is no really effective way to know whether the car is being driven or not.