I balanced the carbs last week and found out in the process that my fan does indeed work and cuts in fine when the engine is hot, how do I know?
There I was, head burried in the engine trying to get the screwdriver on the balencing screw (for the umpteenth time that morning) and all of a sudden...VRRROOOOOOOOOOOOOOOOOOOOOOM,

there was that initial reaction of jumping out of my skin, leaping away from the bike thinking "F*CK what have I touched" before I then realised the fan had cut in as it's supposed to!