Serious Rendering Glitch...

Hi, I have a serious issue with rendering and wonder if anybody can help? In the image below, my game view is on the right of the image, and the editor view is on the left. The camera is in roughly in the same spot (its hard to tell, but it is). There are two issues...

1. In the editor view, I am starting to see corruption in my textures. As pointed out below on the left, the same panel runs along the length of the corridoor and in some parts od the same geometry / texture (they are prefabs), there is corruption.

2. Also, when you play the game and go to the same spot, the screen is filled with black and pink squares that flicker and glitch as you move around. This can also be seen in other locations in the scene, but it is at its worst here.

The scene used to be fine, I haven't changed the geometry, apart from adding more geometry to other areas of the scene, so I have no idea what's causing it. Does anybody have any clue what might cause this to happen? Any help greatly appreciated.