Thank you all for your advice. I appreciate it.
I don't know whether the 5 minute render was from scratch or not. I think it was, but I don't know for sure.
Yes, I'm working from an exact copy of their file, so whatever overrides they have, I should have.
It takes so long to even display the number of triangles that I haven't done this test. :-(
To be honest, I've given up on Radiosity, deciding that I will just use Final Quality Renderworks (FQRW) instead and things have been a little better (though I've still had to run the renders overnight). However, my latest file is about 30MB and now even FQRW is taking far too long to be usable. Last night I set it to do a FQRW render and after 6 hours it had only done 9%. Even Fast Renderworks takes 15-20 minutes which makes it really time consuming to review each change.
Could it be that my files are more complicated than they need to be? I don't have many textures in there though I do have a lot of lights. My scene is mostly extrudes and hardly any NURBS. There are no image props and the textures I'm using are all 40k or less. It's just one room - does a filesize of 30MB indicate a problem? When I see other people's VW files they are rarely above 5MB. Is 30MB unusual for a single room space?
Many thanks again,
Chris