As the originator of this thread perhaps I should now close it with the resolution. Although when running Word and checking 'Tools|Addons & Templates' none were found listed - this was in fact the cause of the problem.

Many months later, and checking the folder structure in Explorer, it was noticed that within MS Office there was a subfolder named '97 Templates'. It seems that when Office 97 was upgraded to Office 2000 this subfolder was retained, although not listed within Word when running.

Deleting this subfolder immediately solved the problem. My thanks to everyone who assisted in solving this rather irritating problem.