Intermittent random lights failure

Hi, I have a 2003 renault megane convertible and I'm at the end of my tether with random intermittent lights failure. Sometimes they are fine, others times I indicate or go around a round about and front beam goes out other times rear and dash goes out for no reason. I have been to two garages who have drawn a blank. I tested them recently in preparation for an mot and when turning the column stalk switch from side lights to beam the rear lights seemed to flicker. There seems to be no pattern to this failure and no one seems to have a solution. Many thanks in advance