[Africa]

The angle of the photo does give the Snake the 'penetrating' look of a montpellier snake, but I have checked both options in the book Fauna Iberica Reptiles volume (quite detailed book in Spanish published by the Spanish Natural History Museum from Madrid).
Montpellier Snake can be found in any dry habitat and it is found in some areas of Cantabria. Dark/melanistic specimens are found occasionally in the northwest of Spain in the larger specimens (they can reach almost 2 m and I have seen impressive skins of this size).
On Grass Snakes, they occur all over Cantabria, has a wide habitat use, including close to water but also forest, and are one of the commonest snakes in N Spain, melanism is relatively common in the north of Iberia and melanistic specimens tend to have pale head markings - just like yours. As to size in that area males reach 70 cm and females just over 1 m.
After all this, I am inclined to think it is more likely that yours is a melanistic grass snake. Checking the head markings in my book again the look of a grass snake is pretty penetrating too and the scale markins under the eyes seem also spot on.