I phoned my local Porsche centre about this again this morning. The Service Advisor there stated categorically that 'misting or light condensation' is totally normal. He explained that there are ventilation holes in the headlamps through which the water enters. It is designed this way. They are plastic headlamps which are not designed to be airtight or watertight.

He said that this condensation evaporates by itself but that if there is any left when the headlamps are operated then the heat from the headlights speeds up the evaporation process anyway so the misting/condensation should disappear even more quickly.

He said that the reason why people in other countries may not experience this condensation is simply because the temperature in their country is warm enough so that the condensation doesn't form in the first place or if it does, it evaporates away instantly. I think this is the most logical explanation why rennteamers in warmer countries have never noticed this condensation. I think the only way they could experience it (despite the warmer air temperature which would normally evaporate away any condensation) is if they have near to 100% relative humidity i.e. the air is already so saturated with water that the condensation cannot evaporate away anymore.

He did add that if there is a build up of a quantity of water in the headlamp (i.e. like filling up a container) then this was not normal. That issue should be looked into by a dealer.

However, misting or light condensation on the inside surface of the headlamp is totally normal.

He also said that numerous people have been calling them asking them these exact questions and that this has been the advice they have been consistently giving.

I also asked him whether there is any risk of corrosion etc of any of the metal parts inside the headlamp if this condensation remains in there. He said no.

He finally said that the dealership checks the operation of the headlamps as part of the routine service anyway and they also check that the ventilation holes are unobstructed.

He said not to worry about this at all. It's normal. Hope this puts people's minds at rest! It did mine.