Material Leaking over two faces - Blender cycles

In Blender Cycles I have 2 materials assigned to 1 mesh. 1 material is assigned to a certain area - as with the other. It seems that the materials are merging together, where the two sections meet. How can I stop this?

Do you have subsurf modifier, if so add edge loops or creasing to minimise stretching of mesh
Separate the mesh at that point

Supply example blend

Ill give that a go :slight_smile: