Quote - Hi!

Would be most grateful if someone could point me in the right direction regarding this matter, if you look at the attached picture you se that I get a very weird looking phenomena with GC enabled.

The only thing that differs in the render settings are GC.

Light = 1 point light

Strange, looking at the background alone shows the "With-GC" background being grey, while the "Without-GC" background being white. GC alone should never turn any grey into white, so there must be something wrong going on in your background shader.

For your material: Usually you do not GC normal maps, unless you created them that way (e.g. using some more esoteric software like gegl). At least that is the case for the usual image formats (png & such). I am not sure about PSD files but i guess they should not have GC neither. I.e. set the "Custom gamma value" in the image_map to 1, not to "use gamma value from render settings" and that should help with the plastic skin.