Are you sure ? This a quote from Car Builder Solutions (I know they are trying to sell their module, but I would be surprised if they weren't telling the truth:
NEW IVA REAR FOG RULES
In June 2013 the rules for switching on and off your Rear Fog Lights changed. Now, the Rear Fog lamps must only be lit when the Dipped Beam, Main Beam or Front Fog lamps are lit. The Rear Fog Lamps may continue to operate until the other lights are switched off. The rear fog lamps must then remain off, even if the other lights are switched on again, until they are deliberately switched on again. This is to prevent people driving off to work in the morning with the rear fog lights glaring after forgetting to switch them off the foggy evening before.