Quote "To help out the job there are also two overflow holes too allow for free overflow to the supply tank."
these 'holes' are incorporated to allow fuel to spill back from the supply tanks into the main tank. The Transfer pumps have a rate of flow greater than the the engine driven pumps to deliberately prevent the supply tanks from emptying whilst the main is transfering. There is a 'trick' where a nose high attitude will spill fuel from the main (at certain levels) into the supply tanks without transfer pumps on.
Not sure what amber caution from the main tanks you are on about, the only caution from the main tank sensors will be quantity discrepancy driven, loss of sensing, and transfer pump dry or inoperative. Certainly nothing to do with low fuel quantity...that is from the supply tank systems.
Should both transfer pumps become inoperative due to failure, lack of fuel to transfer, or switch selection/CB failure. the engines will continue to draw fuel from the supply tanks. Should an engine driven pump fail, the supply tanks prime pump should be selected on to feed the engine.
Others have explained the supply tank low fuel warning systems very well....there are 2 independant systems....both have had their problems in the past but the likleyhood of 4 cautions and warnings failling in the same sortie at the same time as the pilot misreading 3 seperate fuel qty indications or taking no action would seem unlikely. I certainly included fuel as part of my regular scan procedure.
As aircraft and units have been withdrawn from the new National service fuel has become a critical factor in task profiles, it is burning a hole in the mind of all police pilots during the sortie. 95 ltrs of fuel was drained from this aircraft, if it is being suggested that it was 'stuck' in the main tank, the pilot and crew would have had to ignore so many visual and audio warnings unless again it is suggested that all of these systems failed on the same flight.