Just came upon this thread and was interested by some of the input. From a 744 point of view, and the A330 may be different in detail but not the philosophy, could we agree:
Assuming an "Aft Cargo Fire Warning" at approx 25000ft the Emergency Checklist would require firing at least one bottle into the aft hold, the second being discharged just before touchdown.
Once again apologies for not being type specific but the 744 cargo hold fire detector is in fact a device that measures the visibility between two lenses to detect smoke (no smoke without fire is the theory). This has proved to be slightly unreliable when carrying fruit from a hot climate which has caused misting when the cargo temperature cooled in flight, clearly not an issue here.
Firing the bottle actually creates a mist and the fire detector will now continue to indicate a fire as the visibility has now been severely reduced by the discharge.
Only indication now as to whether you actually have a fire in the hold is the temperature in the hold and you can bet that all eyes were on that gauge and cabin crew were feeling the floor temp of the aft cabin.
25000ft/ 75-80 track miles to touchdown without speedbrake so LGW is perfect, lets forget about other suitable airports.
Touchdown at LGW and Captain orders an emergency evacuation, slides deployed and he would expect the Cabin Crew to do the evacuation to the max, there really are no half measures, either an orderly rapid disembarkation down the steps or an emergency evacuation down the slides.
Congratulations to all for getting the ship home, it really is more complex when you are in that situation.