Wino,
The cost of having an accident apart from the human tragedy, is very often an airline going out of business. Where are Pan Am, TWA, Valujet, Swissair, etc now? A UK airline can get one hour more out of cabin crew per duty than they can get out of flight deck crew. If they are rostering to maximums like this to draw the last drop of blood, then they surely will have an accident.
Aircrews, both flight deck and cabin, usually want to fly (it earns them money), they usually want to be productive (job security), and they usually want to have a life (dont we all). If the crews are happy with the rostering, then it is probably a good safe system. If they want to work more, then it is probably inefficient. If they are fatigued, unhappy and permanantly knackered, then I personally don't want to be flying with or on that airline.