The issue with the textures only appears to be an issue within the Maya software. I rendered a frame of the crappy black leather to illustrate the problem to find that mental ray has produced a lovely image of a cracked leather cushion.
I was beginning to think that the procedural texturing tools in Maya were worthless, especially as Daryl could not help me to resolve the issue. Even though I wasted a lot of time in trying to get the procedural texture right I am glad that the system does work when rendered, although it is annoying that Maya does not seem to offer an accurate.
As set design and texturing are not the focus of this assignment I shall not do anymore work on these models, even though the jodhpurs and pants look like cushions.