So, reasonably happy with the fire in my last image... (Comments welcome!)
Unfortunately it is not quite to the standard I had originally hoped, but just in case anyone is interested, here is the OSL code and node set-up that achieved this effect.
A lot of the result is down to the geometry, so starting with a tapered flame-like shape is probably going to help your cause greatly. Also, the proximity of one of my scene lights removed some of the colour variation (the hot white at the base), which was added back in using the compositor for the final image.
Additionally, in compositing, the alpha mask was augmented to get rid of the two horrible splotches on the side.
So if anyone does try this and make any improvements to this, please let me know.
