Electronic discharge lamps can pick up enough power and store it in internal capacitors to make them flash due to transformer and capacitance effects of having two cables running next to each other so just forget about the flashing.
Because electricity is invisible to the eye some test equipment is normally required to fault find. Sometimes one can be lucky and find lose wires and you could with main switch turned off try gently pulling on wires at switch and lamp to find fault. The other method is stab in dark and change something just in case like the switch. But finding faults that way is very hit and miss and likely best option is to call an electrician who will likely find the fault much quicker than you and disturb far less and if you value your own time likely best option.
Warning since you have had flashes from energy saving bulb wires may still be live enough to give you nasty shock even with the fuse/MCB turned off. If you do want to DIY use main switch on consumer unit not just the individual trip. And do something to stop others switching it back on again.
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