Ah, thanks both of you! (I think).
The example render had the smooth modifier on, without that it's even worse. I've tried converting to a high res triangle mesh from a lower res image but basically I think I'm stuffed, as it were. Ho hum.
Looks like the dither idea will suffice, it'll make the ground look sort of "mole-hilly" !!

Thanks for the suggestions though guys! I might have something interesting to show you soon.

cheers!