Hi guys thanks for the advice.

In the end I just went with a simple shadow catcher and added a few pieces of geo to break up the shadow at key areas.

Honestdom, I'm guessing this is similar to parallax normal mapping which if I remember correctly is a normal map, but duplicated with an offset so that when the viewer rotates the view the first map moves at a different speed to the second thus creating some very convincing depth. I know the tech is a lot more complicated then that. We had a coder looking into this a few years ago for one of the games we were working on but it's not very cost effective for a real time render.

Thanks again guys

Pete B