the best solution i think to find out where the cable is coming from, most probably from a socket outlet in the same room and just replace the whole cable with the desired length. with no junction cables you will be more safe and you can plaster as you wish. Don't plaster on bare cables tough...
If you have not touch anything than:
the switch you are turning off is an rcd or mcb?
if it is an rcd than there are some brands that when you reset it, it goes in the middle position (not fully down) and than it does not reset until you switch it fully down words than in the up position...
Here in Malta we pay for the power consumption, therefore we pay for the wattage used and not even power factor could help to save bills. But my question is what's the difference of installing a low voltage light fitting (with a transformer) other than connect a 240V fitting direct to the main...