I'd often wondered what this shape on the map was. Having walked through it discovered that it was a greyhound schooling track complete with fences.
The cache cannot be found at the listed co-ordinates although they are a massive hint to the simple puzzle below:
N51 21. (White+Black&White) (Orange*Black*Orange)-Red
E0 16. (Orange-Blue-White) (Blue+Black+Orange)*Black&White