JB007. I do get your point. Absolutely, and if you had LHR as the alternate and had taken 20 mins holding and then diverted to one of the aforementioned airports no big deal. If the airports were filling up rapidly and your fuel was going to become a serious issue then declare a fuel emergency. I still don't see the problem. Besides, only 9 aircraft diverted that day and the fire started at 0840 and was under control (ie: out at 0900) How many times has that happened in LHR in the last 20 years? I would guess that the only other times that LHR has closed has been in bad weather and on those days, hell you might even have AMS as your alternate. (I stand to be corrected though)
With regards to the FODCOM then take your 20 mins holding.
Betterfromabove. If you look carefully, I'm not saying you should plan to land with 30 mins final reserve fuel. You would still have a few hundred kilos extra for your alternate (LHR), your holding fuel (20 mins) and your contingency fuel.
Heathrow Director. The point of nominating LHR as the alternate is only to save fuel on days of fine weather and no operational problems. Of course if you have an emergency the Noise Abatement goes out the window.