Ice forms on the inside of my windscreen and takes ten minutes to clear: what is actually causing that?

It is not normal, and it is a straightforward diagnosis: there is too much water inside your car.

Interior frost is condensation that froze. Warm air holds moisture; when the car cools overnight the moisture comes out onto the coldest surface, which is the glass, and below freezing it forms frost rather than mist.

A car with a normal amount of moisture in it gets a little mist. A car with a wet interior gets what you are describing, which is why your neighbours do not have it. And the fact that it is worse after rain is the clearest possible clue.

So find the water. In order of likelihood:

Wet carpets and mats. Feel them, and lift the mats and feel underneath. A soaked underlay holds litres and releases it slowly for weeks.

A leak. Blocked drainage channels around the windscreen and sunroof are the classic, and they push water into the footwells. Door and boot seals next.

Wet things left in the car - coats, umbrellas, gym kit, a dog.

A leaking heater matrix, which usually smells sweet and leaves an oily film on the inside of the glass.

Dry the interior properly and the problem largely disappears.

Change the cabin filter before anything else. Mine was four years old and packed solid, so the blower was moving almost no air, which makes both the demist and the drying useless.

Twenty minutes, cheap, and it made a bigger difference than anything else I tried.

For clearing it quickly and stopping it coming back, the thing most people do not do: use the air conditioning in winter.

The compressor dries the air. Running it alongside the heat gives you warm dry air rather than warm damp air, and it clears glass far faster than heat alone. Most modern cars engage it automatically on the windscreen setting, and plenty of people turn it off in winter thinking it only makes things cold.

The full demisting method:

Air conditioning on, heat up, fan high, on the windscreen setting.

Recirculation off. This is the one people get wrong. Recirculating keeps the damp cabin air going round; you want to draw in outside air, which in winter is much drier.

Open a window slightly for the first minute if it is very bad, which vents the moisture rather than moving it about.

And two preventative habits:

Clean the inside of the glass properly. A film of residue gives moisture something to condense on and makes wiping smear. A clean screen mists noticeably less.

Do not leave the car with a wet interior, and crack a window for a few minutes when parking somewhere sheltered after rain.

Wet umbrella in the footwell every day will do it on its own, no leak required.

On drying it out, because half measures do not work - I chased this for a whole winter before finding a blocked drain.

Lift the mats out entirely and dry them somewhere warm. Then press a hand into the carpet underneath, especially the front passenger footwell, which is where leaks collect.

If it is wet, find the source before drying. Common causes: leaves blocking the drainage channels at the base of the windscreen, a blocked sunroof drain, a perished door seal, and a badly fitted windscreen. Pour a little water in the relevant channel and watch where it goes.

Dry it properly, which takes days. A dehumidifier in the car with the doors shut for a few hours is dramatic if you can run an extension lead. Otherwise a fan heater on a dry day with the windows open, repeated.

Then keep something absorbent in the car over winter. Moisture absorbing bags for cars are cheap and they genuinely help once the source is fixed. They are useless while the carpet is still soaked.

And check the boot as well as the cabin, a leaking rear light seal or a wet spare wheel well produces the same symptom and is the one nobody looks at.