sounds like you have a switched neutral and not a switched live
make shure the supply is switched live
easy to check using a neon screwdriver
take the bulbs out and take the switches off the wall or just one of them
then test to see the switched supply lights the neon
if it dosnt you have a problem with switched neutral ....
to confirm this test just go to the bulb socket with the switches turned off
and test the poles inside with the neon driver one will light
all the time and wont be switched on and off
the flashing is coupling over the switch to neurtral or to wetness or basicaly just the weather
as the neutral is basicaly just earth { its earthed at the power station}
if this isnt the case
you maybe have a dampness or other water somewhere
but im shure it will be
the energy saving bulbs strike at a low voltage level
unlike light bulbs
and will flash every so often due to capacitance
if live is already there {leekage to earth or neurtal }
OR there is a nail thru your cable somewhere this could also cause it
but its unlikely i plump for switched neutral
AND an amount of seasonal dampness {winter rain's}
as for fire risk
its more likely if there is a fire youll
be electrocuted instead by a live wire falling out the celing !!!!
that cant be switched off by the switches
i hope i helped