I think that so many of you are missing the point. If an aircraft suffers from smoke, fumes, mist or and other unannounced substance in the air then carry out the SMOKE AND FUMES Emergency drill.
If the front end put on their masks and declared an Emergency then why was that not carried out in the cabin. I would rather breath Oxygen for ten minutes as a precaution than be killed by some poisonous particles in the cabin air conditioning.
Saying that because no one was injured the cabin crew performed their job correctly is ridiculous.
I am assuming that the whole crew has been grounded pending a full investigation by BA and if need be by the CAA?