It was Desktop Windows Manager at 25-30% CPU usage, after some digging around I read stories of laptops with their display off causing this problem to occur.
I should have given more background to my problem: I run a desktop as a workhorse machine with nothing but power plugged in, I remote desktop into the machine to use its power when needed.
So I have no screen plugged in, and in this is where the problem lies, similar to the laptop problems I mentioned earlier.
With no screen plugged in dwm.exe shoots to 25-30% CPU on idle, once a screen is plugged in (even when the screen is off) the problem disappears and CPU utilisation returns to normal 0-5% on idle.
Now the question is why is this happening in Windows 8? the same system running Windows 7 had no issue.
Graphics driver problem?