<<Some of the "advice" my friend was given during his command training in realtion to fuel, and delays (in the London TMA in paticular) was to declare a medical emergency if things were looking iffy>>
One particular airline did that with such regularity that they were tumbled. I flew with that airline from Los Angeles to Heathrow a little later and a pax was taken quite ill. Incredibly we held for 20 minutes so the crew must have had the frighteners!
I can only ever recall Virgin and BA being short of fuel, never any other airlines. Is this still the case nowadays??