This winter for the first time I've seen and tried 'pre-icer' (Tesco, Halfords etc) which you spray on at night. It doesn't prevent ice forming but make it much easier to get off, and stay off, the next morning.

I have used pre icers in the past,got some from a pound shop they where selling them off.Orginal price was expensive.They do work not as much ice on the windscreen.In winter I always use a soft brush to get writ of snow and a scraper and de icer.I would be a bit weary of using warm water on a frozen windscreen but if it works for you fine.

I have been using warm water for years as well. Never had a problem, except when it re-freezes as it has in the recent cold weather. But I'm not keen on de-icer and scraping, warm water is much faster to clear the car, and more environmentally friendly I suspect.

I have also been suffering from ice inside the car this winter, never had this trouble before but I suspect its because I do short journeys and the inside of the car doesn't really warm up. De-icer is also not good for inside the car, the fumes get up your nose somewhat!

Lukewarm water works very well, I also tend to keep neat screenwash (have the Costco one that goes to -36c neat) in a squeezy spray bottle in case of refreeze.

I would be very careful using it on door glass, however, as water penetrating the door gubbins and re-freezing can result in locks freezing wither shut or open until it melts again (managed that twice on an old 300zx - then spent 30mins with the engine/heater running until the door would stay shut).