The fan on my car heater has broken and would cost hundreds to mend. I don't need it most of the time as the heater itself works, but after I have scraped frost or ice from the outside of the the windscreen (sometimes with the aid of a de-icer spray) the inside of the windscreen needs more than a wipe with a cloth as it just mists up again.

It is ok after about five minutes of driving but it is not safe to drive before I can see out (!) and I don't want to run the engine for 5 minutes while stationary, with the cost of fuel what it is.

I have two thoughts for a solution but both have mixed reviews. First, a plug-in car heater, which I would run for about five minutes with the engine off and then unplug it before driving.

Second, a dehumidifier containing bentonite (not silicon) which - if it works - should absorb all the moisture so that there will be none left to form a mist over the inside of the windscreen - or other windows for that matter.

What is your view of these products? You are the only opinion I trust.