I have a few thoughts on the way this thread has developed. Was the fog actually forecast or as I believed it went below limits for Cat 1 unexpectedly, or while the aircraft was airborne. Surely all airlines have to train for Cat 3, we do most of it in the simulator, but both Captains and F/Os have to do 1 practice Cat 3 in the aircraft, during line training, before they become Cat 3 cleared, it seems unlucky that this ocurred before the trainee Captain was so cleared. Would a scheduled service Company really hold a aircraft on the ground if the weather was only forecast to go below Cat 1 limits? I pity the whole crew for the results of what I consider to be a perfectly reasonable decision, i.e divert if the planned destination has gone below limits. We are briefed to carry an extra 30 minutes hold fuel for destination if the weather is or is forecast to go below Cat 1 limits, thus holding over destination is possible, and likely, prior to an approach or diversion. It is always difficult to stay away from emotive words, turbulence, thunderstorms, bad weather etc during a PA, and my Company has a PA booklet for flight deck, to help in what to say and when to say it, currently being revised.