I will be interested in any responses here. I was on the return of that flight from JNB to LHR on the 3rd and we were also delayed by approximately 12 hours. I did a live chat with an agent at the time and they told me the delay was due to crew sickness at LHR and gave me the link to claim compensation. (I have a screen shot of that conversation if you think it would help jd_)

Interestingly when we did leave the pilot said the delay was weather related. I do know however that a number of the crew members in JNB had food poisoning so not sure if they extended the outbound delay to give them more time to recover.

I submitted my claim for compensation and expenses but have just had a holding message reply so far.