Well, I suppose you could get really drastic and take AWLS apart piece by piece, testing until you narrow down the cause.
Thanks once again for giving me things to try

Using the BAIN installer I have established that Meshes: QTP3 Windows Chimneys or Textures: Mages Guild Orange or Red Chimney QTP3 causes the load to hang. I also get the hang if I use the non-QTP3 texture so it seems to be something to do with the Chimneys.
I don't understand what could be causing the problem, but I may try and play without including the AWLS chimneys (even though I have Smoke Textures enabled) and see how it goes. Perhaps if it goes well, I can try re-install Chimneys at a later stage and see if the problem is still there.
I have presumed that AWLS meshes and textures should be installed after UOP and QTP3 - thought it worth mentioning, just in case.
As ever, happy to try anything else anyone can think of.