E46 headlights flickering ???

[Who Me]

My 2003 E46 tourer has developed a fault of the headlights flickering on and off sometimes. This happens when they are switched off at the switch.
Tried to read some other comments about this and people talk of the ballast and light connectors being corroded but this is not when the lights are switched on, the switch is in the off position and they seem to start to do it for a few minutes then it stops for a while then few days later its doing it again.
Ignition is on when this occurs.

Any help or thoughts appreciated.